Specter, The (Vintage Paperback) by Joan Lowery Nixon

Seventeen-year-old Dina is fighting cancer and is angry at the whole world. But when Julie, a nine-year-old survivor of a car accident, becomes Dina's roommate at the hospital, there's no time for Dina to keep on being angry. Because Julie is frightened. Desperately frightened. She's sure that someone caused the accident she was in ‒ someone who will return to kill her. Now she's insisting on being with Dina all the time.

But by befriending Julie, is Dina making herself the target of a dangerous killer?