Our dog (purebred shih tzu) used to barf all the time..drove me crazy. The vet seemed to think it was a food allergy so we switched to an expensive food..it's a salmon and rice mix. The barfing stopped so that must have been the issue. The dog gets no human food whatsoever and if it does find a scrap, even the tiniest bit, it will end up sick the next day so we are very careful if we drop something.
It does seem like the shih tzus are especially prone to tummy troubles, my friends with shih tzus or shih tzu mixes have reported their pet going through these illnesses much more than other dog owners.
May I ask the brand of your dog food?
Thanks everyone for the replies, the vet is not in today due to New Year's, as soon as the office is open I'm going to run everything by him, but it does make total sense to stick with ONLY her food for now, give it a few weeks, and see how she is doing. If we still have problems after that, I can look into another brand or homemade, or see a specialist.