Since she began her career writing for Seventeen magazine, Gayle Forman's evolution to author of best-selling young adult novels was not a stretch. Her latest book, "If I Stay," has been translated to the big screen and is in theaters this Friday. It is the story of young Mia and Adam's love, music and choices. The 44-year-old lives in Brooklyn, is married and the mother of two young girls. The sequel to "If I Stay" is "Where She Went," available only in book form so far.

Q: Was there anything you didn't expect when you saw "If I Stay" translated to the big screen?

A: I saw a lot of the drafts of the screenplay. I saw the casting decisions, and I was on set for quite a bit of it, so I really started to get a strong sense of how it would be. Of course, you don't really know how it is all going to hang together ... and where the emotional punch was going to hit. I was surprised by some of the scenes that really affected me. It wasn't the sad stuff, but it was really the kind of moving stuff.

There is a sequence early on when young Mia first finds a cello. She is playing and she sounds horrible, and her parents are downstairs with their hipster friends and Kat, the mom, is like, "Oh my God, I am going to claw my eyes out." Denny (the father) is sitting there quietly, and the next scene he is outside her door and you see this sort of silent transformation as he is about to change his life for his daughter. That part just makes me weep. It really snuck up on me. And the music. You can't know how amazing that stuff is going to come alive until you actually see it and hear it.

Q: Did you write the song lyrics and did you have any input into the music that was so much a part of the story?

A: I didn't write the song lyrics. There are song lyrics in the sequel, "Where She Went," that I wrote, but no. They really thought about it and kind of put the call out and got all these different songs in that were written by various songwriters. We had a lot of talk about what to rename the band as well. We went through hundreds and hundreds of options (laughing).

Q: Your main characters are teens, so as you write them, do you relate to them as a mother, a friend or are you them?

A: I am all of the above. When I started to write "If I Stay," Mia just kind of came to me. She was fully formed and she was 17 and she was a cello player. She was also very, very serious. Very worldly, wise. (Producer/director) R.J. (Cutler) calls her an old soul. As I sat down to write her and she came out of me, I was a little taken aback because she seemed more mature on the page than I am. I still talk like a 16-year-old valley girl and here was this character who felt more mature than me!

I also feel incredibly maternal toward my characters, especially since they are young. Then I obviously see bits of myself in them as well. It was interesting having actors play them because those feelings transfer to them. I feel very maternal in particular toward Chloe (Grace Moretz) and Jamie (Blackley). Don't mess with them (laughing).

Q: Are your daughters old enough to worry you will write about them or to feel competitive with your characters and the time you spend with them?

A: I have written a picture book that is based on my daughters. You know, my youngest one likes to tell everybody, "Mommy wrote 'Best Day Ever' about us." Which is true. My oldest daughter is constantly giving me ideas, so we sat down at one point to try and write this book together. But I don't think they are there yet. They are not old enough to read my stuff. My oldest daughter, who just turned 10, I think some of her friends are starting to read "If I Stay."

Q: You deal with some heavy themes in the book like loss and choices. Were you concerned or did it just evolve with the story?

A: When I started writing the book, I wasn't sure it would be young adult and neither was my agent. I am glad we decided in the end that it would be. I think (young adult) has really evolved and basically encompasses anything that is a coming-of-age story. There are lots of really wonderful, fun YA books that are set in high school and about the high school experience. I am not reaching back to my high school time to kind of relive it and mine that for material when I am writing these books. I am usually working out stuff that I am dealing with now. For whatever reason, every time I sit down to write one of these books, the characters who arrive to tell the story tend to be between the ages of 17 and 22.

Q: That is very interesting.

A: Yeah, there's a bunch of reasons. I always joke that I am still 16 in my head. I think there is something else to it. As we get older, we tend to think it is less OK to be vulnerable and to feel what we feel. It's kind of bull. We all still feel things pretty deeply. It just becomes less socially acceptable to express that. I thought about what would happen if I wrote about people in their mid-40s, and I would have to write about people who are hiding behind layers of subterfuge to mask their feelings.

You do that in YA as well. You have characters who are avoiding what is going on and acting in ways out of their self-interest and you, the author, knows what is going on and they don't. But I find the thought of writing about me, a 44-year-old-woman, I don't know if I would be able to get the voice right. Every time I think I am going to do that, I lose interest.

Q: Were your own parents as freewheeling as the ones in the book and movie?

A: They weren't that freewheeling. I was the third kid and they were just really busy and it was the '70s, but my parents always trusted us. They said, "We trust you and you listen to the voice in your head. You know the right thing to do."

When I was 16 I was an exchange student in England for a year. When I came back from that the idea of me being a kid under their rules was over. But I never abused that. My parents weren't young cool punk rockers, but they were pretty cool about giving me some room to expand my boundaries and like Mia, I didn't abuse that. They know their daughter and know she has never done anything too crazy. They trust her. There is a mutual trust there.