TODAY, unlike every other day, Nicola Benedetti has not played the violin. Truth be told, she hasn't even got it with her. "The guy who looks after my Stradivari," she starts explaining before pausing and correcting herself. "Not my Stradivari, the Stradivari I play, has been telling me for months now he would like me to leave it with him for 48 hours and I just look at him as if he is mad."

But she's in Glasgow today to do interviews and tomorrow she'll be in London to do the same. And in the days to come she has to learn a new violin concerto composed especially for her by jazz musician Wynton Marsalis. So today, this in-between day, seemed as good a time as any to hand the instrument over.

"Also I've been practising so much last week that this thing on my neck is giving me a bit of trouble." She shows me a little worry knot of angry, puckered skin, on the place where she rests her instrument. "So, two days not aggravating it is a good thing."

It's a decent excuse, I guess, though a little part of me is disappointed. After all, the last time I met Benedetti she played her violin just for me. In her slippers.

But that was in the living room of the Walton-on-Thames house she was staying in at the time and that was 12 years past – almost half her lifetime ago. And, really, she doesn't need to establish her musical bona fides any more. To be fair she didn't then either, having already played Glasgow's Royal Concert Hall and London's Albert Hall at that point (she was 15). But since then, well, what hasn't she done? Won Young Musician of the Year aged 16, picked up a six-album recording contract worth £2m, been given an MBE by the Queen. She's played a few concerts too. OK, more than a few. Come to think of it, wasn't that her at the Commonwealth Games opening ceremony last year?

And on they go. This month it's London and Edinburgh. Next month, Glasgow, Perth, Inverness, Aberdeen, Edinburgh again. And that's not to mention performances in Dublin and around England.

Today, though, she's here, in a Chisholm Hunter store in the Silverburn shopping centre to promote the launch of a Raymond Weil watch. The watchmakers are sponsoring her September Italy And The Four Seasons tour, so fair's fair. If nothing else, it gave her the chance to stay at her parents' house last night. Normally you'd find her in London where she lives with cellist Leonard Elschenbroich.

I've arrived here with a copy of that long-ago interview. I guess I'm hoping to chart the difference between then and now. Between the confident, bouncy girl who was fresh out of the Yehudi Menuhin school, who talked about how much she loved Michael Jackson and wanted to play the Carnegie Hall, and the young woman (just about to turn 28) in front of me today.

"Oh my goodness," she says, leafing through the magazine. She stops at an image of her standing in her cluttered teenage bedroom. "My mum could not believe I allowed them to photograph this room!" Look at it! That's literally how it was the whole time."

"You look so moody," her PR says, peering over her shoulder.

"I looked moody the whole time," Benedetti says.

Was she a moody teenager then Nicola? "Not really." She's not a moody adult either. What she is, I'd suggest, is a sweetly earnest young woman deeply in love with music. Maybe the biggest change, she suggests, is "the deepening of my all-over artistic and cultural understanding and knowledge and world view".

"I'm sure at that age," she adds, indicating the teenage pictures in front of her, "I wouldn't have stopped to think as much as I am now. I'm thinking of so many hundreds of things and saying very little. I always say the people I admire most are the ones who relentlessly deepen their knowledge of the world until they die, but never lose optimism and hope."

This is the kind of person she wants to be. "I'm always trying to deepen my knowledge and sometimes I learn things that are very heartbreaking and difficult. A knowledge of human behaviour. And of course, realisations within the language of music. What sort of struggles Brahms, Tchaikovsky and Shostakovich went through, their trials and tribulations. All of these things – if you let them in – tend to hurt a little bit. You feel a bit of that pain. And if you try to process all of that in turn that adds to what you are able to express in your playing."

There is something almost adolescent about the way she is grappling with the joy and terror of being human. People can do wonderful things, she says, and yet they can be terrible too. She struggles with that knowledge.

So what is the question she is always asking herself? "Am I being a good person?," she answers. "Am I being the best person I can be?"

It's really as conscious as that? "Yeah, I ask myself that a lot. Because, I think, playing can make you very self-absorbed."

She frames everything in terms of music. The main difference between the 15-year-old Benedetti I met all those years ago and the woman in front of me now, she thinks, might be the fact that it's no longer just about the violin for her; it's about music, about its pains and pleasures. She spends hours every day – today aside – practising. There is always room to improve.

It's not like she practises every day and gets incrementally better, though, she says. "It's not linear. Very up and down. I have moments that feel like a deep struggle. 'Will I overcome this?' My partner Leonard and my mum and people who know me very well, they just recognise now that's my way, that's how I get better at something."

She once said, I remind her, that she falls in love with composers through their music. "All the time."

Are there any she just doesn't get on with? "Sometimes it happens. I never pay attention to myself when I'm having that feeling because I think all that is, is the mix of me and that composer at any given time is not one that's working. I'm in the mood for someone else, basically. If I'm coming across a piece for the first time and I don't particularly like it I'll be quiet about it, not start thinking, 'I don't like this.' Because the next time I come to it, it might be my favourite piece of all time."

Is she quiet in the rehearsal room, though? What's the power dynamic between conductor, orchestra and soloist? "I tend not to have problems on that front. Obviously I'm opinionated about how I feel things should go but very rarely will a conductor suggest something that I can't see some light in. My biggest issue is if I'm having to work with someone whose behaviour I don't respect." Such as? Conductors who are rude to their musicians, she says. Or even to the guy who opens the door for them.

"I always notice those things and I find it very difficult to ignore it and think, 'Oh well, they're great anyway.'" The guy holding the door is a person just like Beethoven was a person, she says. "Those kinds of things bother me sometimes. Only then would I get on my defensive stance and go, 'This is how I want to do it.'"

But that's not the norm. The norm is a democracy. The relationship between conductor and orchestra, she concedes, not so much.

Is classical music a sexist world? "Far less than so many others. You only have to look at my job and how many female violinists there are these days. There's a surplus of excellent violinists ..."

Not so many female conductors, though. "... I'll get to that ... And no hesitation in accepting us. If you were to take a broad sweep at the moment you wouldn't be criticised for thinking that women excel at instrumental playing and perhaps less so in conducting. But that could very well be only down to opportunity and largely down to prejudice. But we'll see."

She is aware of the power structures in place. Look at composers, she says. "The only female composers I play are living today, so why is that? Were there no genius women composers in the last 300 years? I don't believe that for a second."

This is the outspoken Benedetti, the one who has argued for classical music on school curriculums. "Yes, I've said it in all kinds of polite ways and it always comes across as I'm telling the world what to do and I don't know how to stop coming across like that."

But she sees it as a big picture idea. Music offers a part of school that is not so "dead focused on what job you're going to get, but actually deals with the wholeness of the person you're going to turn into".

It's difficult to quantify, she admits, but those schools that include music and creative activities all say that as a result everything rises across the board. She worries away at this idea for some time. Halfway through she even interrupts herself: "I know I'm talking too much." But on she goes. "If I could count the number of times I've heard, 'In our school they decided to have all the children learning choir and can you believe that this, this and this improved in the school?' Yes, I can. I can believe it."

You could call it the El Sistema approach perhaps: Benedetti has been loudly and proudly supportive of that Venezuelan-founded initiative through the Big Noise children's orchestras in Raploch, Stirling and Govanhill, Glasgow.

Her own experience is different of course. The second daughter of an Italian immigrant father and self-made millionaire, Benedetti had her first violin lesson aged four. Encouraged by her mother, she practised and practised, won a place at the Menuhin School aged nine, meaning she had to leave her West Kilbride home to go to London.

Nicola, would you be offended if someone said you had been hothoused? "That means by your parents? I wouldn't be offended. It would just be inaccurate."

Well, you did get opportunities not typical of many childhoods. "I would say that all of that was driven by my desire to play."

Her mum was no pushover and, yes, strict boundaries were laid down. But the person who pushed her to practise was herself.

She doesn't know where she stands on the nature/nurture equation. Of all the factors that might have influenced the woman she is now– class, gender, nationality, parental influence – which would she single out?

She can't, she says, but then adds: "I have two very strong characters as parents. Our family is quite fiery. That has had a huge impact on my attempt to be myself around these very strong characters. But equally I think I've been given a very strong character."

That must have led to some butting of heads, I say. Of course, she answers. "My dad grew up quite impoverished and his understanding of making a success in his life was entirely focused on making money. Understandably. Not just for him but for his entire extended family. He's an entrepreneurial character, very strong-willed and a risk taker.

"But I think for people that take a risk on ideas and keep winning, the wins tend to validate the ideas. And it takes a certain kind of person to say, 'Well, a lot of these wins were just good fortune.'

"My dad had enormous amounts of those validations, so that made an already strong character even more so. And for me to try to explain to him that a success in my eyes can have nothing to do with money and all and could be so far away from earning anything ... He just about understands it now and I've been doing this as my job since I was 15, 16. Yeah, we've had plenty of run-ins, but healthily so."

Every day – except today – Nicola Benedetti plays the violin. She also likes to cook and she's prone to fretting. Living in London she is not tempted to bulk-order in Irn Bru. "Whisky maybe." She's still not played the Carnegie Hall. ("I've had three concerts in Carnegie Hall that have been cancelled at different times in my life. One day I will do that.") She has seen life in Venezuela and India, seen poverty and privilege and is still trying to put everything together in her head. And when she can't, the world of music is her release.

For her there's nothing elitist about classical music. That's learned behaviour, she suggests. "When you go into a school, kids just listen. Somebody's playing a violin in front of them and doing all kind of magical things on this instrument. Basically that is magic to them. You don't have to fight that battle.

"Of course you do with teenagers and older populations. I find it sad if people don't grow into classical music. But I only find it sad because I think – if you only knew what you were missing."

Nicola Benedetti performs with the Oslo Philharmonic at the Usher Hall as part of the Edinburgh International Festival this evening. Her Italy And The Four Seasons tour begins in Perth Concert Hall on September 17