I would absolutely recommend Milk Thistle and Denosyl (Sam-E) as well. Some vets just aren't that knowledgeable or supportive of holistic alternatives.
Here's a good article for you:
MILK THISTLE
I get both milk thistle (Marin) and Denosyl from Entirely Pets:
Marin for Small to Medium Dogs (30 Tablets) Denosyl | Denosyl for Dogs & Cats
Lady has liver disease from ten years of phenobarbital for seizures. Pheno is notorious for destroying the liver over time. I have used milk thistle almost from the beginning and added Denosyl a few years ago when her bloodwork showed her liver was finally becoming damaged.
I also switched her to a homecooked diet for dogs with liver disease at the same time. Within nine months her liver had regenerated and her bloodwork was normal.
I have not seen an organic prescription food for liver dogs, but there are a couple of premium quality low protein foods that people have had good results with.
WELLNESSŪ - Healthy Dog and Cat Food Solid Gold Health Products for Pets - Products
This has great information about diet and liver disease.
Liver | B-Naturals.Com Newsletter