I really need help finding this book title about a girl and her wolf!?

The girl's name was Anna (I think) and she had a sister named Savannah, and I think her dad was a radio dj, and while driving down the road, possibly moving to a new house, they saw a sign for a zoo, which was really a bunch of neglected wild animals in cages, and the girl somehow ends up with the wolf and becomes attached to it, and names her Ruby. Her neighbor poisons the wolf in the end. Any help would be much appreciated!