The day before I meet Pollyanna McIntosh, the Dunbartonshire native was thrown off a Clydesdale horse during a photo shoot for an online column she writes.

(McIntosh is not only an actor but a writer and screenwriter too, and a good one; but more on that later.) "It was the biggest horse I've ever seen," she announces as she sits down to a cup of tea in the G&V Hotel in Edinburgh. "I came off it at the end of the day. I was holding a crown which was very heavy, and it had lots of spikes and diamonds on it and I was leaning backwards and arching my back. It was wanting to go forward and with me being bareback … I had to let myself fall off. So I came down, rolled and my head hit the ground, but it could've been a lot worse."

I am expecting McIntosh might be tired - last night was the gala opening party for the Edinburgh International Film Festival, which McIntosh was attending to promote her recent horror film Let Us Prey, but she arrives looking as fresh and newly made up as a daisy. (A former model, McIntosh falls into the category of people who can look good when we mortals appear to be carrying our life's possessions in baggage under our eyes.) But it wasn't a late night.

"They screened [the film] Hyena, which I'm sure was a very good film, but I snuck out and got a chippy because I was knackered," she declares. Indeed, the evidence was on her Twitter feed with a picture showing her looking out of place in a greasy spoon, dolled up in a plunging, canary-yellow halter-neck dress, with lashings of bright red lippie. "I'd had one of those days," she stresses unapologetically.

So after only a few minutes, I have made some fairly concrete assumptions about McIntosh. One, that she seems willing to go the extra mile when the job requires, demonstrated not least by her feral character in 2011's Sundance hit horror The Woman and her role alongside James McAvoy in last year's Filth, in which she appeared in a sex scene. Her latest film, White Settlers, a horror flick, saw her running through the Borders covered in blood.

Two, this is a woman who lives life on her own terms. Previously, the 35-year-old might have found herself in that screening last night and thought, "I have to stay because this is where I'm supposed to be." But now, she says, "I have that wonderful release of growing up and thinking, 'I can do whatever I want. I can prioritise for myself.'"

And three, McIntosh may be one of life's pretty people (striking and statuesque, her sartorial style today comprises black skinny jeans, white T-shirt, mint pumps and fuchsia lipstick), but she seems as down to earth as they come, with a sense of humour to boot.

This bodes well for our chat. McIntosh's affability stems in part, I'm surmising, from the varied geography of her life, both current and past. As a child, she and her family (she has three sisters) lived in Portugal and Colombia before settling in Edinburgh when McIntosh was nine, where she attended St George's School for Girls. Today, she remains a bit of a nomad and, as such, seems to fit in easily wherever she goes and happily lives out of a suitcase as and when her career requires.

She visits Scotland frequently - she has appeared in Bob Servant Independent and Waterloo Road - but lives between Los Angeles, where she relocated 10 years ago (and where she met, married and divorced American actor Grant Show), and London, where she moved in 1995 at the age of 16 to model after winning a competition and where she's lived for the past two years. But she's back in LA now. Socially, she says, it's more her kind of place, where meeting up with mates usually involves outdoor activities rather than a trip to the pub. It's an independent way of life, so good friends are important. Sure, the LA stereotypes exist; but it is also a city full of creatives, she says.

She copes with the transient nature of her life by knowing what's best for her. "Because the job is still really exciting, and I still get nervous on the first day of shooting. But all the nonsense that surrounds it - that can be on your own terms."

One way in which she finds peace is through writing. Her columns for online magazine Crave are honest, funny and raw. In one she describes the day she lost her virginity at 13 in candid detail - something she never thought she would do. In others, she reveals her weight battles - McIntosh has been anorexic and also three stone heavier than her current weight, during which time she did plus-size modelling and appeared in Vogue as a size 14 - and admits to self-harming as a teenager "and a little beyond".

"I've always written songs, stories and spews of feelings just to get it out," she explains. "I've always had far too much emotion to be Scottish. Although we are an emotional bunch, we don't show it until we're drunk." Then, a few years ago, she started writing screenplays. "This one I'm in development with now is the first one that will actually get made."

It was while working on a film that a producer said, "I bet you can write." He asked to read something. "And the feedback was so great," recalls McIntosh. "I quickly went from incredibly shy to bold, and started writing things so personal."

Her purpose, she says, is honesty: encouraging others to fulfil their potential through recognising their own faults and their own challenges. "That's what I enjoy, from a very female position. I've always been kind of a blokey girl as well, so the script I'm writing seems to appeal to guys as well." Called Perfect, it includes "a bit of gross-out humour", she says. "But not like the way Judd Apatow does it; it's more realistic and quite confessional."

McIntosh reminds me of American scriptwriting comedian and actor Tina Fey, a woman who is attractive and funny yet has broken into Hollywood with female-centric scripts that appeal to both sexes. Interestingly, the lead character in Perfect is a woman comedian "stoner perfectionist" who will be played by McIntosh. "If you stay on that stuff [pot] long enough, you constantly need it to lift you up," she says. It's as bad an addiction as cocaine. It's not an anti-pot film but I do think it's worth making a story which, instead of 'stoning' being funny, is exposing a bit of the truth. Because it's tempting …"

What, the pot? "I'm from Edinburgh," she laughs in response. "I was smoking pot at 13. I'm not Drew Barrymore or anything but I still have the odd spliff."

Crucially, there are parallels in the lives of the central character and McIntosh. Both are self-employed in the arts; both lose a friend to suicide ("A big step in growing up," she recalls); and both have a sister in Spain who is the parent of a toddler at the time they give birth to a premature baby. So when the lead character is called to the aid of her sister - leaving behind her disorganised, career-centred life - she is forced to look after others for a change. "It's about finding that in-between space. It's not about finding perfection; it's about finding the comfort and stability in your own faults and the things you can't control," explains McIntosh.

Is that something she has struggled with herself? "I think we all do to a degree," she muses. "I definitely have no stability in my world; I feel the need to be up and merry all the time. But I couldn't have written this if I hadn't gone through some of the pitfalls she [the lead] finds herself in. So it's probably me a few years ago - and then slightly magnified for the story. As she gets more in touch with herself, it becomes more honest, like: this is the s*** that I hide and this is who I am."

This feels very much like McIntosh - having been through the modelling industry, experienced the highs and lows of acting and emerged from a divorce, she strikes me as a woman who has come into her own. With children featuring heavily in her script, is parenthood a future prospect?

"It's not for me at the moment. I'd love to have a kid. But if I have to adopt then I'd be happy to do that. I'm in no rush. My ex-husband just had a baby [with his new wife] and I found out online a couple of weeks ago. I got a real fright and, at first, was all puffed up and furious. And then it was a good lesson because I realised that, actually, I was happy for them. I thought, 'Why did I react like that?' Because I know I don't want to be with him. I don't want his baby. And I realised, 'Oh, I would like a baby some time, that's why.' I was a bit jealous. Do I want one now? No, but down the line I would really like the option to raise a child, whether it's mine or someone else's."

She acknowledges the power in reaching such a conclusion - and says it feels good. "Right now I don't think I could give a child what it would need," she admits. "I'd want to be in one place, make it my priority, and my career is my priority at the moment."

And is that writing? "It's beginning to look like directing first and acting second. I guess you should ask me that when I've made my first film," she smiles. She hopes it will be her screenplay for Perfect. "I still love to act but I've turned down so many things lately because they haven't interested me. It means I'm broke, but I'd rather be broke and inspired."

Thankfully, she adds, Let Us Prey was a "decent payer", allowing her the freedom to be picky. White Settlers, a suspense thriller about an English couple who move to the Borders, is out now. Though it's not a political film, the current independence debate has seen it described as a "Scottish referendum horror". (If she could vote, McIntosh says, she would back independence.)

"But there's definitely a transition point now," she continues. "I'm loving writing. I'm on the third draft of Perfect and I've got a third of the funding. Just gotta get that cash." She says the last word with a twang. All going well, she says, it would be natural to make the film in Scotland.

Just as McIntosh's career continues on the ascendent, her personal life seems to be falling into place, too. Although she remains tight-lipped who her new American director beau is, it doesn't stop her gushing. The relationship, she says, is "encouraging, stabilising", a "forward-moving relationship for my … own growth". She laughs. "It's really cool to hear somebody say, 'I trust you.' That's a mind-blower. Like, I don't need to worry about you?"

Did she feel held back by past relationships? "I thought I had to fix everybody. I don't have to worry about this one. He can take care of himself.

"It's actually arrogant to be so considerate of other people's feelings because it suggests you have influence." She chortles again. "It's like playing God. It's actually a waste of time. And if you find yourself in those relationships, it's probably so you don't have to deal with yourself, which is quite convenient. Whereas this [relationship], it's the real deal."

I wonder if she feels set free. "Yes, I feel set free to fail. It doesn't matter what happens. There's a stable basis for the whole thing which is trust."

In her mid-30s, McIntosh agrees she's in a good place. Confident but self-deprecating and aware of her strengths and weaknesses, when asked what her ultimate goal is, she replies, "I've got five movies I want to make" (all her own scripts) "and I've written a sitcom which I think is hilarious."

The comedy is based on her modelling experiences, although those days are over now. "I went out with a bit of a bang," she recalls. "The last jobs I did were phenomenal. But I'm grateful for that time. I learned a lot, not least being a skinny model and not being able to eat; being anorexic through work. I can't thank that experience enough for having shaped me and making me grateful for my body. To have been through that so young and to have come out of it - bonus - because now I don't give a damn."

But surely job-seeking in Hollywood must add pressure? "It's always there," she acknowledges, "but I'm lucky in that I'm already kind of tall, deep voice and powerful looking, so it would be weird if I was really skinny now."

Directing is clearly the ultimate goal. "Hopefully I'll learn a lot as a first-time director. I'm chomping at the bit to do that, I feel ready. It took me a while to make that decision but then I realised, 'The time is now.'

"Same thing when you fall in love with somebody. There's no point in waiting to see, you just have to commit. So I want to keep making movies of my own. I don't think I'll always be in them - I'm looking forward to directing one I'm not in - but this one [Perfect] is so personal, I have to fulfil all those roles. I feel weird saying it because I'm Scottish, but yeah, I feel extremely confident about making this film."

Is this gumption from her upbringing or is it the American in her? "Anyone who's survived being in the acting business for over 10 years … you either get there or you die. I feel like I've earned it. Growing up, the experiences I've had and the support of the producers that have come on board. Eventually I had to believe them when they said, 'This [script] is worth being made.' But it doesn't matter if it's a success or not because I have my acting, which I will continue to do and love. I'll keep going forward." n

White Settlers (15) is in selected cinemas across Scotland now. There will be a special screening and Q&A with cast and crew on September 25 at The Cameo, Edinburgh. The film comes out on DVD on October 20.