It sounds funny, Megan, but many dogs prefer to eat cat food. Since it’s higher in protein, fat and calories, it’s more tasty. However, most dogs will still eat their own dog food if they aren't offered another choice. Remember that the nutritional needs of cats and dogs are different, and their foods are formulated to meet those specific needs. Although it is not usually harmful if a small amount of the wrong food is eaten, nutritional imbalances affecting your dog’s health could occur if this continues long term. Dietary changes can also cause gastrointestinal discomfort and diarrhea. If at all possible, when visiting your dad, I would recommend that you take your dog’s food with you and that you do not allow her to go near the cat’s food.