Mockingbird by Kathryn Erskine
Caitlin has Asperger's. The world according to her is black and white; anything in between is confusing. Before, when things got confusing, Caitlin went to her older brother, Devon, for help. But Devon was killed in a school shooting, and Caitlin's dad is so distraught that he is just not helpful. Caitlin wants everything to go back to the way things were, but she doesn't know how to do that. Then she comes across the word closure--and she realizes this is what she needs. And in her search for it, Caitlin discovers that the world may not be so black and white after all.