Fountain of Knowledge

I think the best way to answer your question is ask a ton of 11 year old girls what their favorite book is. If you don't have a lot of relatives or friends with kids in that age range, I suggest contact the principal of your local elementary schools and if you could survey all the 5th grade girls on this question. Then you could look at all the answers catagorically, what genres are most popular, what authors, is there one or two books that come up a lot? Then read these books, see what the stories are about and how these authors captured their audiences minds and go from there. I'd love to hear about how this goes. Good luck.