What kind of food are you feeding her? If there is corn in her food, she is probably allergic to it. You will need to change her to a food that doesn't have corn or what products. Any food on
this list with a protein content between 20-30% is an EXCELLENT food choice with no corn or wheat products. I would personally recommend Chicken Soup for the Puppy Lovers Soul (that is actually an All Life Stages food, not just for puppies) because the kibbles are very tiny and easy for tiny yorkies to manage.
If changing her food doesn't help, you will need to take her to the vet and get her tested for other types of allergies.