When I was a kid I found this big book on mice in the library that covered everything on them then eventualy got one. I was about the same age I think when I had my mouse. She was cool but rats as everyone said do tend to better for a pet you can hang out with.

I'd have her read up on both and then make the decision herself since it's officialy her pet. I had to feed, water and clean mine myself but my parents would check up on it to be sure I did everything for it.