It is a really good idea to test for liver shunt. You must have a good vet.
Sometimes UTIs in Yorkies indicate a problem (but not always so don't worry). The vet will do a bile acid test. You fast your dog for 12 hours (overnight) and the vet takes blood. She will be fed a meal and blood will be taken two hours later. It is a simple test. The normal results are premeal: 10 or below and postmeal: 15-20 or below. The numbers can be lower but you don't want them much higher.