Miracle Vet High-Calorie Weight Gainer for Dogs & Cats - Multivitamin Nutritional Supplement Gel, Omega Fish Oil, Calcium - Puppy, Senior, Prenatal Cat & Dog Vitamins, Supplements for Weight Gain

It’s hard when dogs get older. I foster dogs and cats and use high calorie supplements to help them gain weight. Check out Dyne high calorie food additive and liquid weight gain (https://a.co/d/0hGX6NPg). Not sure how those might work with her food restrictions so definitely read the ingredients. If you get her on a supplement, she should perk up in a few weeks. Plus if you mix it with her food she might be more willing to eat her food. Wet food is also your friend for this if you can get her a low calcium wet food.