Insanity by Kira Moericke

For the past five years, Em Knightly has had the same reoccurring nightmare that leaves her gasping for air. No doctors have been able to help her with these nightmares without leaving her numb or unlike herself…except one, one that sends her to Brier Hall, an old Victorian manor that is now a place for troubled teens.
But there is something peculiar about Brier Hall, something not right. There is a terrible legend about the manor – a legend of true love, death, and magic. A legend of witches and ghosts. But Em doesn’t believe in ghosts…at least not until she meets Casey, a mysterious boy who seems to know something about her that even she doesn’t know. And Em plans on finding out what exactly that something is.