Shame, I feel bad that you and Tila have to deal with this. Loads of Yorkies suffer from allergies and it's usually due to a food intolerance. Have you tried putting her on Orijen Lamb & Apple? An allergic reaction to either of these ingredients is very rare and if her allergies clear up while on this food, you can be sure that the allergen was in her other food. If she doesn't improve on the Orijen Lamb & Apple, I'd get another opinion from a vet who specializes in these issues. If she improves, you can keep her on the Orijen or switch to something with similar ingredients. Just make sure that you don't give her any of the "old" ingredients again.
You might want to try a raw diet too. My dogs are on a raw diet and we don't have any issues. My oldest Yorkie scratched and chewed all the time while he was on kibble, but he doesn't do this on the raw diet. No more bald patches on his legs
