Liver shunts are all too common in Yorkies. In fact, Yorkies are 36 times more likely to be born with a liver shunt than all other breeds combined.
Did your breeder bile acid test both Emma's parents? They still could be carriers, but it's a precaution all reputable breeders should take as part of their heath screening prior to breeding.
Emma does not need to be fasted before her bile acids test. That protocol is outdated.
I've attached a few links for you about shunts in general and the bile acids test.
Portosystemic Shunts FAQ Hepatic Vascular Disorders - WSAVA 2006 Congress PSVA and MVD Research Summary