‘Whirlwind’ is the best way to describe the success of Girl Asleep, in cinemas now.

Since premiering as a play during the Adelaide Festival two years ago, it’s miraculous that stage and screen helmer Rosemary Myers — who’s also the artistic director of the youth-focused Windmill Theatre Company — has even had time to think.

Just over a year after the play premiered to raves (The Guardian called it “as inventive and surprising as its audience”), a film adaptation had won the Audience Award at the Adelaide Film Festival before going on to open the Generation 14 Plus section at the Berlin Film Festival.

It’s a whirlwind on Saturday afternoon when I meet Myers and star Bethany Whitmore, who plays Greta, the girl in question, at a screening in Brisbane. They’re fresh off the plane from Adelaide, part of a whistle-stop tour of Australia doing Q&As to tirelessly promote the film. It may have been euphorically declared that last year was the most successful for Australian films ever, but for micro-budget miracles like Girl Asleep, it’s tougher than ever.

In the film, Whitmore plays Greta, a shy and introverted 15-year-old who is more at home playing with her collection of plastic horses and reading letters from her Finnish penpal (who is also named Greta) than make-up and boys. The strange, new world of teenagerdom, described late in the film as being like “some new person had turned up inside my body and kicked the old one out”, is one that’s frightening and alienating, and one that she’s not sure she wants to go to. However, everyone else around her does. In a bid to, as her mother says, “bring her out of her shell” around her classmates at her new school, her overconfident but well-intentioned parents throw her a party. Set in 1977, there’s plenty of disco, coloured lights, and mini quiches to go around; with guests even entering to a synchronised dance.

But as most teenage birthday parties are, for Greta it’s torture. The awakwardness is both funny and brutally painful. Scenes with mean girls outfitted in ridiculous matching outfits and gazes inspire both laughter and tears, simultaneously absurd and painfully relatable. Retreating to her room, away from the overwhelming madness that’s reminding her of everything she does not want, she falls asleep, dreaming of a fantasy world that’s both comforting and scary, innocent and weirdly erotic.

Myers utilises the common visual motif of adolescence being a forest one must pass through, and of course, Greta finds her way out. It’s a journey that’s a little bit Wes Anderson, David Lynch, and even Michel Gondry, but nonetheless unique.

Myers, a multi-Helpmann Award nominated director, took the reins of the Windmill Theatre Company in 2010, broadening the focus from producing theatre for teenagers as well as children. It’s a shift that saw Girl Asleep emerge. The company is known for its vibrant, distinctive works that intertwine film and theatre references. Myers says that “the cinema is the main artistic medium of the time we live in”, and that Girl Asleep was destined for the screen from the beginning as a result.

The reluctant 15-year-old Greta is played by an adult on stage, but here she is brought to life by 16-year-old Bethany Whitmore. Whitmore talks enthusiastically about Requiem for a Dream and wanting to pursue fashion design as well as acting and filmmaking, and has already amassed an enviable resume. Aged six, her first role was as Debra Messing’s daughter in the mini-series The Starter Wife, also working alongside Judy Davis. “I was so oblivious,” she laughs when asked about the experience.

It was an auspicious start she’s since lived up to, being one of the lead voices in the animated film Mary and Max as an eight-year-old; acting opposite Essie Davis in Melbourne Theatre Company’s production of Cat on a Hot Tin Roof in 2008; as well as starring in Mental and more recently The Family Law, which is due to begin shooting again in Queensland next month.

For Whitmore, who “fell in love with Wes Anderson’s style” when she saw Bottle Rocket, it was her first major lead role, and one she especially related to. The mournful, heartbreaking part of moving from childhood to teenagerdom, a loss outside of one’s control, is something that’s often overshadowed in favour of the restless excitement to grow up. Myers expertly conveys Greta’s shy personality and empathy through the colourful, diorama-like style of the film, whether that be storybook-like chases through a forest or a heartbreaking encounter with her younger self. There’s a disarming fragility to it.

“This sort of role is my dream role,” she says. “(I felt) a lot more responsibility this time. It was really daunting but really exciting.

“I played with my toys until I was 14. I loved getting lost in my own little world.”

Myers is thrilled to have landed Whitmore.

“It was amazing when we found Bethany for the role,” Myers says. “It’s not an easy role, she’s a passive protagonist at the beginning of the film.”

The film was shot in 22 days on a budget of just $1.7 million, a miracle when witnessing the dollhouse-like sets. “Our shoot was quick and ambitious,” Myers says.

That challenge created an energy and an environment that Whitmore believes transferred to the exciting atmosphere of the film. “It was all very much a collaborative environment,” she says. “We were bouncing off each other’s energy.”

It was an energy that was much needed on the long night shoots for the party scenes (when they were “racing against the sun”, as Myers puts it). Next door to where the film was being shot, the young cast had a party of their own in between takes, complete with magic tricks from Whitmore’s co-star Harrison Feldman (Upper Middle Bogan) and a sleepover.

“Everyone on set did it for love and creativity,” says Whitmore.

The film has played over 40 international festivals, and has even snagged a release in the United States in the coming weeks, a rarity for Australian films not associated with Mad Max or boasting international names. Myers, Whitmore, and writer Matthew Whittet have travelled everywhere from Berlin to Buenos Aries to Giffoni in south-west Italy with the film. Whitmore’s attended parties in underground railway tunnels in Berlin (“there was one moment where I just stopped to take in my surroundings,” she says). Myers has been particularly interested to see how foreign audiences engage with the film.

“We had a journalist from Japan who thought that we put the father in short shorts to make some sort of political statement,” she laughs. “I had to explain that it was just what Australian men wore in the ’70s. They could not believe that.”

But all misunderstandings about short shorts aside, there’s no doubt the film has resonated deeply, its story of loss and self-discovery a universal one. Myers puts it simply: “Everyone’s been a teenager, going to be one, or is one.”

Like Greta, we’ll all find ourselves in the forest, lost and scared, but we’ll find our way out, too.

Girl Asleep is in cinemas now.