The 17-year-old actress has been tipped for awards glory for her role as a transgender teenager in the upcoming drama, and admits she has lots of transgender friends who helped her prepare for the role.
She said: "I have a lot of transgender friends that go to my school, who have made the transition over the summer and have changed their names and used different pronouns. So I was used to that."
Elle - who stars in the movie with Oscar nominee Naomi Watts - also revealed she knew the film would be one of her most difficult parts yet.
She told PEOPLE.com: "I definitely knew that it would be a huge challenge to do - I've definitely never done anything like that before."
The actress previously admitted her nerves ahead of the film's release as she hopes to speak for the transgender youth worldwide.
She explained: "I was really nervous not to screw up, because this is for transgender kids out there."
Elle - who transitions to a male character in the film - had to bind her chest with Velcro for the film.
She said: "It's like a sports bra that you wrap around, only it's Velcro. I had to wear one every morning. It hurt so bad!"