American Girl by Wendy Walker

Accepted to MIT, Charlie can't wait to get out of Sawyer, Pennsylvania. Autistic and living with her mother, stepfather, and two brothers, Charlie works long hours at the Triple S deli to save money for her education. When the owner of the Triple S, Coop, is found murdered, everything that Charlie has been working for is put in jeopardy. There are several people in Charlie's life that she would protect to the utmost--which is what Charlie is prepared to do. Who in Charlie's circle is a killer? American Girl is a suspenseful character-centered read with a main character who stays with you long after the last page is turned.