It is not the Royal Canine, the brand, that is probably the issue with her acting differently when being fed that food...it's the protein content. Dogs with liver shunt can not process protein. Toxins build up in their bodies.
Her bloodwork indicates she needs additional testing to rule out LS.
I'm not sure why a vet would say her liver is "small"...however, many vets are not very familiar with shunts.
UT is a wonderful...considered premier for LS and corrective surgery. They also provide the services for much less than found elsewhere in the country.
Here's some more information....
Portosystemic Shunts FAQ
The more quickly you get a diagnosis and treatment if necessary the bettter.
Sending prayers for Chance.