I loved Christopher Pike at that age, for the creepy, supernatural-y when Stephen King was still beyond me.
Literary Buffistas 3: Don't Parse the Blurb, Dear.
There's more to life than watching Buffy the Vampire Slayer! No. Really, there is! Honestly! Here's a place for Buffistas to come and discuss what it is they're reading, their favorite authors and poets. "Geez. Crack a book sometime."
She likes Harry Potter, The Hunger Games and The Omen. She loves musicals,video games, Star Wars/Star Trek and is impatient and easily bored.
For a kid who likes musicals, I'd recommend Better Nate Than Ever by Tim Federle, a fun new middle-grade novel about a kid who goes to Broadway, and Drama by Raina Telgemeier, a graphic novel about a middle-school drama club. Graphic novels in general might be something to look into, actually.
Diana Wynne Jones?
Earthsea?
Seconding Tiffany Aching. Also Jessica Day George, maybe. Possibly Douglas Adams?
Anne McCaffrey's Harper Hall trilogy?
Seconding the McCaffrey.
Oh! Lois Duncan! They reissued most of them -- Down a Dark Hall is my personal favorite, but there are a bunch of thrillery sort of mysteries she might like.
Ooh, seconding Lois Duncan! Loved her!
I can't find my original, hardback copy of Down a Dark Hall and it kills me. Mostly because I would love to reread it. I LOVE Lois Duncan.