Grief changes people.
Brittany used to be a normal teen. She ate like one. She slept like one. And she even had typical mood swings. But finding her best friend dead changed everything.
Grief could explain her loss of apetite and her lack of sleep. It might explain why she sees her dead friend everywhere she goes. But it doesn't explain why everyone she touches develops bruises or why she's attracted to the smell of blood.
And what's with the urges to eat her new boyfriend?