The Bone Dog

Sarah's Gran Gornal is a witch.
So is her Uncle Bryan.
Sarah's parents won't let her have a dog because of the cost of feeding it and taking it to the vet.
Uncle Bryan says he'll make her one that won't need food or the vet.
He makes her a bone-dog. Sarah finds she can make it do anything she wants.
Even bad things that she knows she shouldn't do...
And Sarah starts to enjoy her new-found power...