In 1966, Australian singer Helen Reddy arrived in New York with her young daughter, after being told she had won a record contract.

The record company then informed her that, actually, they had enough female stars already.

But she decided to stay in America to pursue a career in music anyway - and ended up writing and singing I Am Woman, which became the anthem for the women's movement in the 1970s.

It makes for an inspiring biopic, titled the same as her most famous track.

"I met Helen seven years ago and it has been the most blessed, powerful and also challenging experience as well," notes Australian director Unjoo Moon, who was born in South Korea, when asked about the journey of making I Am Woman.

"I always knew that this story would be something that we should really put on screen; it's a story I hadn't seen before, and it's a movie I wanted to watch."

Reddy, who had Addison's disease and was diagnosed with dementia in 2015, sadly passed away in September this year, aged 78.

Moon, 56, says she is "so glad that Helen not only got to see the film but to hear about how much the audiences loved it".

There were also lots of discussions between the filmmakers and Helen about how the feature - which premiered at the Toronto International Film Festival in September last year - would depict her marriage to Jeff Wald, who was also her agent.

Although Jeff helped her get to the top, and they had a son together, he also suffered from drug addiction, and it was a toxic relationship.

In 1983, they divorced. And the film doesn't shy away from showing both the good and the bad bits of their time together.

"The more I got to know Helen, and as we tweaked on the film over the years, I think the nature of the relationship that we ended up showing in the film tweaked along the way as well.

"I remember when we first started working on the script, Jeff was a very different character. I'd not met him at that point; he was really the villain of the movie. When I first met Helen she wasn't even speaking with Geoff, she was still calling him 'husband no 2'.

"Their relationship changed over the years that we worked on this film, and I would hope that this movie actually helped to contribute to that because they had to be more in touch as well."

Moon admits she was nervous about meeting Jeff at first.

"I always felt this movie had to be told from Helen's view and he's such a big character, we didn't want to be distracted by him. So, we really worked on shaping Helen's story first.

"I went to see Jeff; I arrived at one, I didn't leave the table until seven, I didn't even go to the bathroom. He is one of the most fascinating, charismatic people you could meet. He's also very difficult and tough, and he would be the first to admit that.

"But actually, having that relationship with him really helped me to understand why Helen loved him so much, and I think that's what's really important in the movie, not just to see why the marriage falls apart, but what the attraction was and why they were such a great team."

The film is largely about a woman fighting to have a voice, which Moon agrees feels particularly relevant with the Me Too movement gaining momentum in recent years.

She reflects on attending the Washington women's march in January 2017, where hundreds of thousands of people protested, to advocate legislation and policies regarding human rights and other issues.

"I went there to support the cause, but I also went there because I wanted to stand in that exact same spot that Helen stands in at the end of the movie.

"Helen, in 1989, mobilised the women's march; she stands and looks out at that sea of people around the Lincoln memorial, and I did the same thing.

"There was a sea of pink hats and there was actually a sign, which I took a photo of, saying 'Hear me roar' - that actually appears right at the end of the movie."

Moon went on a "huge personal journey on this project, "not only as an artist, as a woman and also, as a mother".

One of the hardest elements for her was that her teenage son Axil, who was only 13 at the time, felt very strongly he wanted to stay at home and go to school with his friends rather than travel to Australia with her, where the film was being made.

"It was really the first time my husband [Dion Beebe] and I - Dion is the cinematographer on the movie - had both been in separate countries from our son. That was a really tough experience for me.

"Often, working women aren't allowed to talk about what it's like to be a mother and how challenging that is and how challenging it is to juggle all these different elements of your life because, as a woman, you're supposed to be able to do it all."

Female friendship is also something explored in I Am Woman; we see Helen's relationship with legendary rock journalist Lilian Roxon, played by Danielle Macdonald, who's known for films such as Patti Cake$ and Dumplin'.

The Sydney-born star, 29, says she cried when she first read the scripts, especially at the bit where Lilian writes the liner notes for Helen's album.

"I was amazed at this story of this woman," she continues. "I knew 'I Am Woman', the song, and I had no idea she was Australian, which is a horrible thing to admit considering I am Australian.

"She had these songs that inspired a generation of women to have voices and to be strong and to have a say. That was incredible."

There are a few things Macdonald would like women to take away from watching the film.

"I would like people to just know that they have a voice and they have a right to that voice, they're allowed their opinions, they're allowed to have their own life and that's an incredibly important thing," she expresses excitedly.

"I also just hope people have fun! I remember at Toronto [International Film Festival] we finished the movie and people were just singing along in the audience, during the credits, and that feeling - I just want people to take that away."

I Am Woman is available to watch in select cinemas and on digital platforms now