Mockingbird by Kathryn Erskine

Caitlin, who has Asperger's Syndrome, searches to find "closure" following the death of her brother, Devon,  at a school shooting incident.  Her father and counselor help her in her struggles to overcome her problems in making friends, understanding emotions, learning her manners, and grieving for Devon. The title is reflective of Caitlin and Devon's favorite movie, To Kill a Mockingbird, which helps Caitlin to relate to others.