Book title help please?

I read this book, and I can't remember the name! It was very odd. The mother had kids, and she killed two of them, and tried to kill the other, but she got away. Her name was Francine but the adoptive parents called her Frances. She meets a boy named Nix and hits it off. She's later confronted by her mother and it's this whole bad situation. Does anyone know name of this?? Please! :)