We always have to seperate Jenny and Buster from each other because of safety issues. Never would I put my dogs together in a room(Except Ginger and Rocky get along in the same room with a bone and they don't bicker with each other) I would seek help from a behaviorist. Please do not get rid of Gracie for this incident. If I were you, I'd seperate them from now on and go to your breeder and ask them questions about her behavior if it continues. IMO, no dog should be alone in a room with a treat together unless you know that they won't go after each other.