book recommendation for girls

I am looking for some good book recommendations for my younger sisters. One is in 8th grade and the other is a sophmore in high school. Over the years I have bought them some of the core must-reads, like The Giver and Lord of the Rings, etc. But I would really like some recommendations that have amazing women or, even better, girls as protagonists. They are at an age where every other book they read lately is a Gossip Girl type novel and I really want to get them back into GOOD adventure/fantasy/mystery books with women and girls in, or sharing, the important roles. If the book is by a woman that is another plus as well.

I recently came across the Land of Elyon book series which looked good but it is hard to know without reading it and apparently those books are recommended for grades 4-6. They are both very good readers so they even read book that are considered a few grade levels above them and beyond (one of my sisters has been reading War and Peace on and off for like 3 years, haha).

I am sure this group will be able to help me a bit. Thanks for your help!

x-posted to feminist_lit and feminist