In addition to pulling the hair off of her back legs - does she also chew or lick any of her paws? Bc that would be another cardinal sign of allergies. Humans cough/sneeze with allergies...dogs have their paws itch and it drives them to bite and lick them to make the sensation go away.
Things to ask yourself...how long has she been doing this and when did it start? Is it seasonal or year round? Is she itchy? Do her eyes water a lot?
If you do suspect allergies, do read this thread:
http://www.yorkietalk.com/forums/die...tart-here.html