The University of Tennessee is a world renoun leader in Liver Shunt Research. There are pages on their site full of info about LS...
I am confused at this point.... the best thing I would tell you to do is to get a second opinion... and to do some research... this is from:
Portosystemic Shunts FAQ Can a shunt be diagnosed with a liver biopsy?
In animals with shunts, the liver is smaller than normal because it is atrophied from poor blood flow. On a liver biopsy, the tissues appear shrunken. Some of the vessels are very tiny, while others multiply in an attempt to improve the blood supply and drainage. These changes are called hepatic microvascular dysplasia.
Hepatic microvascular dysplasia (HMD or MVD) can also occur in dogs without liver shunts; therefore, other tests are needed to be determine if a shunt is also present.
Concerning the elevated AST and ALT: These values can also increase due to toxins (general term) and by that I mean anything from the dog ingesting mushrooms to getting too many vaccines at one time... and everything inbetween.
I have never seen prednisone prescribed for Liver Shunt.
Why was your dog on long term metronidazole? and for how long?
You say she 'acts well'... is she 100% or is she still having neuro symptoms? Exactly what symptoms was she showing?
More history: When was she last vaccinated, what vaccines did she get, has she ever had any reactions to vaccines?
Best next thing to do for her would be a Bile Acid Test.
I am not convinced she has a liver shunt.... and I wouldn't give the pred until sure of what is going on with her.
I am not a vet.