I agree having the vet run a panel, it could be thyroid. You can add Magic Meatloaf to her feedings. Do not free feed, you need to know how much food she is eating per day. A good quality kibble will also add weight, California Natural, Canidae, Wellness, Chicken Soup for the Dog Lover Soul etc)

A peanut butter filled Kong a few times a week always worked for our fosters

Lori