EW asks the actress  about her new film, ''The Perks of Being a Wallflower''

By Sara Vilkomerson
Updated August 10, 2012 at 04:00 AM EDT

Stephen Chbosky not only wrote the novel The Perks of Being a Wallflower, but he wrote the screenplay and directed the film, too. That’s unusual.
In terms of being true to the book, we couldn’t fail. And that’s a relief. It’s always scary when you know how much something means to other people — you don’t want to mess with it.

How did he persuade you to play Sam, a rebellious and popular high school girl?
At our initial meeting, he said, ”Okay, not only is this going to be one of the most important parts you play, you’re also going to have the summer of your life and meet some of your best friends.” I thought, ”That’s quite a claim. Who is this guy?” [Laughs] Everything he said came true.

I’m assuming it was a fun shoot?
Who knew Pittsburgh was going to become one of my favorite places in the world? When I first arrived, I was like, ”Oh my God, this is going to be awful — we’re here for seven weeks? There’s nothing here!” And then it worked out perfectly. [The cast and crew] all lived together in a hotel, and all the rooms were connected. We ate together every night, played music and games. A lot of barriers come down when you’re living together.

How hard was it to master an American accent?
Before I started on the movie, I lost a lot of sleep over it, I have to tell you. I’ve watched movies when actors don’t get the accents spot-on, and it immediately takes you out of the moment. So I really felt like I had to get it right. I worked with an amazing voice coach, and we went through every single word and every single syllable and really hammered it.

You recently wrapped Sofia Coppola’s The Bling Ring, where you play a fame-obsessed teen who robs celebrities’ homes.
I’m partly filled with dread and partly filled with excitement. It’s weird to play this crazy girl. If people find it difficult seeing me with an American accent, wait till they see this.