Not only does Margot Robbie have the challenge of bringing to life notorious figure skater Tonya Harding in I, Tonya, but she also has to play her over a 29-year age span.

The film follows Harding from the age of three all the way through her forties, and Robbie plays her from 15-44.

“I’d never done that before. I mean, that’s a huge age span to jump between, especially when you’re doing an indie film you’re not shooting it chronologically,” she tells EW. “Some days I was 15 for the first half of the morning, then I’d be 23, then I’d be 40 and then back to 15, so it took a lot of prep to keep that straight. But it was a wonderful challenge because you get to map out someone’s character arc over decades and you can kind of see what was their childhood was like, how did that influence the person they then became, how did the incident and her fame, for good and bad, influence the person she then became in her 40s.”

Robbie, who received SAG and Golden Globe nominations for her performance and won the Critics Choice Award for Best Actress in a Comedy, says the script immediately pulled her in. “I was captivated. It was a bizarre, unconventional, crazy, fun, sad script and it felt very original. It was like nothing else I’d ever read before,” she says. “Of course once I realized it was a true story, I was definitely hooked.”

From there, Robbie says the challenge was overcoming people’s assumptions about Harding, particularly while playing her over a significant span of time. “How do you make people forget what they think they already know and just get lost in the story?” she asks.