Frozen Charlotte by Alex Bell

Dunvegan School for Girls has been closed for many years. Converted into a family home, the teachers and students are long gone. But they left something behind... Sophie arrives at the old schoolhouse to spend the summer with her cousins. Brooding Cameron with his scarred hand, strange Lillias with a fear of bones and Piper, who seems just a bit too good to be true. And then there's her other cousin. The girl with a room full of antique dolls. The girl that shouldn't be there. The girl that died.