John Green's been accused of a heavy reliance on the MPDG, as have movies like Garden State, (500) Days of Summer, and even Breakfast at Tiffany's.
So why is Stella in FML not a classic example of a manic pixie dream girl? I had a lot of fun writing Stella. You only get to meet her in one of the story lines because of a choice that Simon Cross makes early on, but her effect on his life is profound.
The thing that makes her unique is that she's not there to wake Simon up. She's not there to fulfill all his dreams and lead him by the hand through life. She's got her own life to lead. She's got her own desires and dreams, and she doesn't have the time (or patience) to sit there and make Simon's dreams come true.
Stella is a real person. She meets Simon and they run around like crazy through the party, but she's got her own story. In fact, she's such a huge personality that it was difficult not to let her run away with the book.
I think you guys are going to fall in love with Stella as much as Simon does. She's a one of a kind character, and definitely not a dream.