If your mother in law is going to take care of your dog again, put the dog ina crate and call a taxi to take you and the dog to her home. Explain to her with emphasis that this is very important to you. If she refuses to honor your request to crate your dog, find a boarding kennel or someone else to watch the dog in the future. Don't let one woman's carelessness and thoughtlessness ruin your peace of mind or bring harm to your dog.