Also, I have seen a child's book about sex in Christian book stores. It was written simply so that a younger child can understand what sex is about. The one I saw was illustrated (not like you think, though! lol) but it is about a married couple who have a baby and it just explains how the baby was made.
Being young myself, I think that you should begin talking about it with her now. If she doesn't hear it from you then she'll get it from the bus or school. Personally I learned from the bus in 1st grade. I really wish my mother would've talked about it with me. And now she regrets that she didn't. Your 9 year old may sit there and roll her eyes or giggle, but she's listening and she'll think about what you said before she decides to have sex!