Hmm.. Do you know what test your vet used for hypothyroidism? Without contradicting your vet or anything like that, TSH tests are extremely inaccurate. To have her thyroid properly diagnosed you need to get a full thyroid panel. TSH, T4, free t4, and a couple of others. I think there are 6 different tests overall. Ideally, you could see if your vet would send the blood sample to Dr. Jean Dodds. She's the leading hormonal specialist in the US and all of the tests plus her personal interpretation of the results costs about $65. The lab itself is called Hemopet. You can google them for more info. I like that Jean takes into account the age, breed, and size of your dog. Most vets don't so what labs consider the normal range can be too broad for your dog. The hemopet site has step by step info on how to send the sample and all that, if you're interested in that. Jean herself has been so, so helpful with my dog and her test fees are so much more reasonable than anything your vet could offer.
As for the Canidae, it is not prescription food. My dog eats nothing else, although he's only 2 and healthy as a dog can be. When I got him he was on Iams and Nutro and I thought he was healthy. Then we started Canidae and the difference is amazing - now I really know what healthy looks like..
I can almost guarantee that your dog would love this food. It is a dry food. Since I discovered it I've persuaded many friends and family to give it a try and even the most picky eaters LOVE this food.. I think it's because it's more meat, no fillers. The first few ingredients are chicken, lamb, and fish. Compare to even the Royal Canin foods where one of the top ingredients is corn or other grains.
If you go to www.canidae.com you can go over the ingredients, find a store that sells it, etc. They even give an explanation for why each and every ingredient has been included in the food, and all ingredients used are human quality foods. It is a little more expensive but you'll find that your dog eats much less of it than other foods because there are no fillers. My dog was eating about 5 cups of Iams per day when I got him and he was still losing weight (he's a very slim athletic build). Now he eats 2 cups of Canidae daily and is in perfect health. I worked it out and the Canidae comes out to be about $5 extra per month, compared to the Iams and Nutro. It took a while to get used to feeding him so little, I was petrified that I was actually starving him, but that's not the case.
There are two different formulas of Canidae. The All Life Stages formula is meant for dogs of all ages, based on reasoning that dogs have never been able to choose puppy or adult formula in the wild. The Platinum has added glucosamine and chondroitin (sp?) for dogs with joint trouble and weight problems...
Anyway, I hope that helps. Like I said, I can't praise the food enough. I just couldn't believe the miracles it did for all of my parents' dogs, particularly the one with the joint trouble..