I'm Not Her

Rachel has a new life. She's living in a new town, attending a new school, and making new friends. She's living in a new house with a mother who works long hours and is never home. Her father is living miles and miles away in her old home town. She talks to him weekly but rarely sees him.
And her sister, her twin sister Sam, is the reason for all these changes. Sam, the closest person in the world to Rachel, decided to shoot up the parking lot on morning at school.
Now, Rachel is trying to put her life back together. She's trying to deal with the guilt. Was it her fault? Were the signs there but she was too blind to see them?
What if everyone at her new school found out? Or Jase, the cute boy she works with at the local kennel?
How is she supposed to get through this?