Liver shunt/MVD is the first thing that I would suspect if she's already had a liver shunt. I know several people who have yorkies that had a liver shunt repaired and then year later, they aquire another one. It's not uncommon. Miko has a liver shunt also, and before he was diagnosed when he was a pup, he used to salivate also, particularly when he was stressed. Maybe it's just stress, but if I were you, I would have the vets do another bile acid test and possibly blood work. Go to this website and join this group...
http://pets.groups.yahoo.com/group/L...d_MVD_Support/
Everyone on there is wonderful, and you'll be able to see the statistics of how often they get a second shunt or aquire MVD after the first shunt is fixed. It's not often, but it does happen...I don't know the exact percentage. I don't want to scare you...I'm just surprised that the vets are dismissing the idea about it being the liver so quickly without doing further testing. Please keep us updated. I pray that it's nothing serious, and that it's just stress or something that will pass.