Have you read the books? They really are good!!! This is one of those things that I cannot wait to share with my kids. They're still a little young (almost 3 and 5 1/2). They have seen scenes from all the movies, because I enjoy them so much. But I know the stories very well, and I make sure they don't see certain parts.
Keep in mind that each book is one year long. Harry and his friends are 11 in the first book, 12 in the second, etc. The books are all told through Harry's eyes, and the author did an amazing job of writing each book from the perspective of a child of that age. (In book 5 they are all 15 years old, and much of that book has to do with emotions of a 15 year old. Amazing!)
When the books first came out, I often heard people say that if the child were old enough to read it by him/herself, he/she was old enough to read it. That being said, I really can't wait for my kids to be old enough for me to read it to them!
At 8 years old, she's probably old enough to read it to herself, so she's probably fine. But I would read it with her or at the same time so you can talk about it with her and so you don't miss out on the fun!