Has she had a bile acids test? Liver shunts are very common in Yorkies. In fact, Yorkies are thirty-six times more likely to have a liver shunt than all other breeds combined.
A bile acids test, then a Protein C test, and then a scintigraphy, are the tests that need to be done before invasive procedures like liver biopsies. Also, don't waste your money on ultrasounds as they are only 80% accurate according to the University of Tennessee, as low as 60% according to Dr. Center.
Most vets don't know enough about liver shunts. Where are you located? Vet schools are usually a better option.
Here are some good links for you:
The Univ. of TN College of Veterinary Medicine - Portosystemic Shunts Hepatic Vascular Disorders - WSAVA 2006 Congress