I'm sorry, zooeysmom, I know that is frightening news. It's only anecdotal but maybe my experience will be a comfort to you.
My bichon/maltese mix, Minnie, had elevated liver enzymes first noticed I guess when she was around 11 or 12. Not drastically elevated but the vet noted it. She recommended 'wait and see' at the time since Minnie seemed in fairly good health overall, only some aging related slowing down etc. Significantly, feeding a special liver diet did not change the numbers nor did she do well on it (I now realize it was that crummy canned Science diet stuff vets carry - so no wonder, really), so the vet said go back to her previous diet, and don't mess with it.
Minnie had the elevated numbers for the rest of her long life and the vet said that many dogs do develop slightly elevated liver numbers as they age -- and it can simply be age-related. The risk of compromised liver function seemed to be greatest when considering any sort of surgery or general anesthesia. So, elective dentals were out and when she simply had to have an extraction at age 14, the vet warned me of the risks but said the misery otherwise for Minnie made the risk worth it. She monitored her very carefully through the oral surgery and used a different kind of anesthesia if I remember correctly. Minnie had a very hard recovery from that extraction -- quite different from an almost breezy extraction of several teeth when she was 10. I knew she could never undergo any other surgeries.
Still, she enjoyed generally decent health until shortly before she died at age 17 years 3 months.
All this to say, I hope that Zooey's elevated liver enzymes are due to aging and that perhaps it is somewhat of a maltese or small breed phenomenon, too. I don't know, but the vet did not seem to be fazed by it. I don't know if Zooey's are greatly elevated or slightly but significantly like Minnie's. I am sending you warm wishes that Zooey's liver is showing signs of age, but that she will be essentially OK with gentle management.