Flying In Place by Susan Palwick Book

Emma is twelve, a perfectly normal girl, in a perfectly normal home. With a perfectly normal father...who comes into her bedroom every night in the hours before dawn. Emma will do anything to escape. From the visits. From the bodies. From the breathing. Even go walking on the ceiling--which is where Emma meets Ginny, the sister who died before she was born. Ginny, who knows things. Ginny, who can fly...