There are multiple causes for liver disease. Liver enzymes can become elevated from medications, toxins, inflammation, infectious causes, parasites, endocrine disorders, and more seriously cancer.
It does not have to be a death sentence, but the fact that your vet said that they were the highest liver enzymes he has ever seen is not a very optimistic prognosis.
I would put her immediately on the herb Milk Thistle (silimarin) at a human adult dose. Milk Thistle is available at heath food stores and some drug stores.
She should also be placed on Hepatic Support (which contains choline and inositol among other hepatic protection agents) and Denisyl (contains SAM-E). These latter two should be taken at the highest dose tolerated and should be available from you vet. The herb Burdock Root is also helpful and should be given at a human adult dose (from a health food store).
It is important to keep her eating. If she has a good appetite your vet can supply her with a prescription diet called Hepatic Formula. I hope this helps!
Also, he said that he's never seen liver enzymes that high before in his career.