Mockingbird by Kathryn Erskine

Good and strong
and beautiful . . .

Ten-year-old Caitlin's world had always been black and white. Anything else was confusing; but her brother, Devon, helped her understand. Then tragedy struck, and now nothing makes sense. As a girl with Asperger's syndrome, Caitlin turns to what she does know--textbooks and dictionaries. And after reading the definition of closure ('klo-zhar), she realises that this is what everyone needs. In her search for closure, she discovers that black and white are surrounded by shades of grey, and that those are beautiful and necessary for healing.