Straydog — Kathe Koja

Rachel is happiest when she's volunteering at the animal shelter, especially after she meets the feral collie she names Grrl; they're both angry and alone. When a teacher encourages her to write about it, Rachel finds another outlet for her pain and frustration. But writing about Grrl is much easier than teaching Grrl to trust her. And when Griffin, the new boy in school, devises a plan to spring Grrl from the shelter and bring her home, Rachel finds that the dog isn't the only one who must learn to trust.