Have you tried her on any grain free foods? I really really am against "lite" or "weight control" foods. They're just chalked full of more fillers (which equals more carbs) and less meat/protein. Just looking at the Nutro Lite ingredients makes me want to cringe:
Rice Flour, Lamb Meal, Ground Rice, Rice Bran, Dried Plain Beet Pulp, Powdered Fiber, Natural Flavors, Soybean Oil (preserved with mixed Tocopherols, a source of Vitamin E), Poultry Fat (preserved with mixed Tocopherols, a source of Vitamin E), Yeast Culture, Calcium Carbonate, Sunflower Oil (preserved with mixed Tocopherols, a source of Vitamin E), Potassium Chloride, Monocalcium Phosphate, Taurine, Dried Kelp Meal, Choline Chloride, Ferrous Sulfate, Zinc Sulfate, Vitamin E Supplement, Ascorbic Acid (source of Vitamin C), Manganous Oxide, Biotin, Garlic Flavor, Calcium Pantothenate, Niacin, Copper Sulfate, Vitamin B12 Supplement, Riboflavin Supplement (source of Vitamin B2), Glucosamine Hydrochloride, Vitamin A Supplement, Pyridoxine Hydrochloride (source of Vitamin B6), Thiamine Mononitrate (source of Vitamin B1), Chondroitin Sulfate, Calcium Iodate, Vitamin D3 Supplement, Menadione Sodium Bisulfite Complex (source of Vitamin K activity), Sodium Selenite, Folic Acid.
The very FIRST ingredient is rice! That is wayyy to much carbs and useless fillers! Where is the meat?! The protein content is 14.00%, which I find RIDICULOUSLY low. I think that's the lowest I have ever seen in any food, actually. I find the nutrient analysis on the food absulotely shocking. No wonder she can't loose weight on this. That's pretty much like putting an obese human on a diet of rice, french fries and white bread and expecting them to loose weight. I really do wonder about vets sometimes. I also don't follow any of their nutritional advice. You're right about Science Diet, it's even worse.
My suggestion is to find a grain free, low carb and high protein food for her. Something like EVO, Orijen, Wellness CORE, etc. I think you'll find a big difference. It's all lean meat, high protein. For example, here are the ingredients to Innova EVO:
Turkey, Chicken, Turkey Meal, Chicken Meal, Potatoes, Herring Meal, Chicken Fat, Natural Flavors, Egg,Apples, Carrots, Tomatoes, Cottage Cheese, Alfalfa Sprouts, Dried Chicory Root, Taurine, Lecithin, Rosemary Extract, Vitamins/Minerals, Viable Naturally Occurring Microorganisms
Also, about the vet's comment on canned food, I think that's totally bogus. Neither canned or dry food do anything for dog's teeth at all. Although, I personally find canned food much healthier than kibble for the following reasons; a) higher moisture content b) usually more meat and less grains c) not as processed. The only thing that helps dog's teeth are things like raw meaty bones, not dry nuggets.
Good luck with your pup! Hopefully she'll be recovered and at a healthy weight soon!