Unfortunately there are so many different GI issues in yorkies. I would never try to guess. I have been through a lot with them....often you end up having to scope them to find out what the culprit is.
There is a GI test that is sent to Texas A & M that often will help diagnose ...here is a link about it:
https://vetmed.tamu.edu/gilab/
I am sorry I didn't see this before. How did the vet visit go and how is Keeva?