DarkLady I'd also like to add in Harry Potter, Hunger Games, The Mortal Instruments (and the spin-offs), Lunar Chronicles and Vampire Academy (and its spin-off). If your niece doesn't like reading about violence then this definitely not the book for her at the moment. I've been reading books of this genre since I was 13 including books with much more violence or much more detail to gore. I was 14 when I discovered this series and I still love it a year later.
Shay This book is a young adult book. Here are some suggestions: "Fablehaven"series by Brandon Mull, "I'd tell you I love you, but then I'd have to kill you" series by Ally Carter, "The Selection" series by Kiera Cass, "The Peasant Queen" by Cheri Chesley, "The Named" series by Marianne Curley, "Princess of the Midnight ball"series by Jessica Day George, Shannon Hale books, "Eragon" series by Christopher Paolini.