Series where the main character influences the angel and demon?

Hello everyone,

I started reading a book ages (years) ago about an 'ordinary' high school girl who ends up with two guys fighting over her. One is an angel and one is a demon and they're both trying to convince her to go one way or another. The twist was that she was some sort of rare human who could influence people around her, and by hanging around her the angel was becoming less good and the demon was becoming less bad?

Does anyone have an idea what the book might be?

EDIT: I think I was thinking about Personal Demons by Lisa Desrochers!