I'm late on this, but happy Halloween! I've spent the weekend reading Jezebel's scary story contest and getting chills. Our apartment windows rattle loudly in the wind and our radiators clank at random intervals, so I may not have picked the best environment in which to read these.
As a kid, I loved ghost stories. I figured out their spot in the Dewey decimal system so I could read the entire collection at my school library. Eric has pointed me in the direction of some good adult ghost fiction, and I continually search for new haunting novels. Here are a few from my past that you may feel like re-reading or recommending for your niece who is definitely brave enough to read ghost stories: