book with black and white cover about orphans??

I read this book several years ago, my mother had checked it out of the library and since then I've been trying to remember the name. I remember it was two girls, one would terrorize the other by banging scratching and screaming on the door at night. I think the main girl was mute. At one point, the main girl had gotten locked in the kitchen(?) after other girls tricked her into breaking a jar of jam. I know at the end, both of the girls die in a fire caused by the main girl. It might've had black and white illustrations in it, it was a very big book (at least for my age at the time). Please help I've been losing my mind over this book!!

This is Thornhill by Pam Smy.