I think I read the first Harry Potter when I was 7 or 8, and if she works her way through the series slowly, I think they'd be fine. I think I was about 11 when I read Order of the Phoenix. That said, I don't think they're all that dark and advanced as the series gets later on - even the dark books have a lot of great happy things

Also that SUCKS that your state tried to ban them from libraries. Dude, America.