In the Skin of a Monster by Kathryn Barker 

Three years ago, Alice’s identical twin sister took a gun to school and killed seven innocent kids; now Alice wears the same face as a monster. She’s struggling with her identity, and with life in the small Australian town where everyone was touched by the tragedy. Just as Alice thinks things can’t get much worse, she encounters her sister on a deserted highway. But all is not what it seems, and Alice soon discovers that she has stepped into a different reality, a dream world, where she’s trapped with the nightmares… Read more.