I'm looking for a book I read when I was a kid. It's about a girl who get's left behind on her island when the rest of her family leaves. She wanted to stay with her brother, but he ends up dying and she's alone. She befriends a dog who she names Amaroq. People come to the island but she hides from them in a cave. Eventually they catch her and take her to a rehabilitation center where they try to teach her how to talk. She has a friend there named Shay, but she ends up being taken away because she wasn't getting better. I forget how the book ends, so if anyone knows the name I'd really appreciate it.

The first part of your description sounds like Island of the Blue Dolphins, not the last part though.