Rain Reign by Ann M. Martin
Summary from Goodreads
In her most powerful novel yet, Newbery Honor author Ann M. Martin tells the story of girl with mental/emotional challenges and the dog she loves.
Rose Howard has OCD, Asperger’s syndrome, and an obsession with homonyms (even her name is a homonym). She gave her dog Rain a name with two homonyms (Reign, Rein), which, according to Rose’s rules of homonyms, is very special. Rain was a lost dog Rose’s father brought home. Rose and Rain are practically inseparable. And they are often home alone, as Rose’s father spends most evenings at a bar, and doesn’t have much patience for his special-needs daughter.
Just as a storm hits town, Rain goes missing. Rose’s father shouldn’t have let Rain out. Now Rose has to find her dog, even if it means leaving her routines and safe places to search. Rose will find Rain, but so will Rain’s original owners.
Hearts will break and spirits will soar for this powerful story, brilliantly told from Rose’s point of view.