I would have to strongly disagree with the vet on this.
Any Yorkie who has had seizures needs to be bile acids tested.
Liver enzymes in a blood panel don't have to go up until the liver is considerably damaged (liver cell death...).
It is not normal for a dog to seize and if it is liver shunt, it is best to catch it before it early... I would most definately have the bile acids tested.
In fact, it is a good idea for every Yorkie over 20 weeks old to have a bile acids test anyway just to make sure there is nothing wrong because LS is so common in the breed. This is according to Dr. Center, developer of the bile acids test.
I'm sorry about your pup.
By the way, my Yorkie didn't show many symptoms of an issue and her bile acids are very high (with no diagnosis).