The girl who was supposed to die

In my book there's a girl named Katie Sagebrush. Katie is facing a lot of conflicts right now in this story. Katie has some mental issues. She was recently tried to be token away by a mental hospitalist. The hospitalist had said some things that made Katie feel like she was getting killed. She doesn't know who she is or what she is really doing so before they revealed her name everything was just clueless. It was very confusing but it still made some sense. This book gets very interesting when she kills the man.