First of all, enzymes will not always be elevated when there is a liver shunt. I found that out recently with one of my pups who I have had for 7 years. He suddenly developed bladder stones and during that surgery, the found a shunt. He has had lab testing done yearly since he came to me and never had ONE elevation in anything at all...and he never had symptoms that one would expect. This is more common than people realize.
Since it is the only enzyme that is elevated, I might be inclined to wait and retest as the vet suggested. Of course, it certainly won't hurt to go to a specialist. You don't have to go out of state to do that. I would find a board certified specialist in your area. I know everyone touts UT and that's all ok but there is travel involved and LS surgery is not rocket science. Many many surgeons all over the country do this surgery successfully. As I said, I just recently had one of my pup's shunt repaired and I was so grateful that the place was close by. Of course, his came up suddenly so I honestly did not have time to even think about where I would have it done. His surgery was fine...and he is fine now!
You also could just ask your vet about doing bile acid testing.