I'm 32 and I still love reading kids books and young adult books! (I was most of the way through my Masters in Education when my son was born with cf and I left the program.)
There's:
-Margaret Peterson Haddix Shadow Children series (4 books)
-LM Montgomery Anne of Green Gables Series (9 books) + Chronicles of Avonlea series (2 books)
-The Sister's Grimm series (about to come out with the 9th book in the series)
-Harry Potter is always wonderful (and long, so it might take her more than a day to get through one) (7 books)
-Percy Jackson series
-The Ender's Game series is spectacular (8 books).
-Nancy Drew
-Redwall series by Brian Jacques
-The Time Quartet by Madeleine L'Engle
-There's always The Hobbit and The Lord of the Rings trilogy for her to grow into. (The Hobbit was one of my favorites at that age.)
-When she's a little bit older (or if she's at a higher reading level now), the Robert Jordan Wheel of Time series is great
-Also, books by Judy Blume, Lois Lowry...
-True Confessions of Charlotte Doyle (Avi) -- not a series, but good nonetheless, and he has a ton of other great books
-You also might want to check out The School Library Journal (http://www.schoollibraryjournal.com/) for new books that are out for that age group.
I hope this helps! If I think of any others, I'll post them.
Thanks.
Erin