I'm of the opinion of you have the language to digest mature concepts and the patience to sit through literature about it, the additional exposure can only be positive.

These are bestsellers from an author of young adult fiction so it's not exactly subversive counterculture. I think the only limiting factor is the girl's own interest, and there's no harm in offering one to try. As an English teacher I can say that age is the ideal time to challenge a young reader to open up the boundaries of reading practice.