Hello and welcome to the forum. We have a lot of threads about diet for dogs with liver disease. There are too many to provide links for each one but if you type 'liver' into the search box it will return all the relevant posts. You may well find some of them useful. Some of them contain advice about using the filters on the Dog Food Directory to source a suitable product and may contain the results of previous searches. This one
might be helpful. There are some suggestions for wet foods here. This thread
includes advice from David on the relevant issues and what to look for when selecting a suitable food.
The cold pressed foods tend to fit the criteria for high fibre and low fat (particularly the ones with brown rice), moderate protein but as copper is rarely listed you would need to speak to the company about this.
If you are inclined to home cook for your dog it can be a good way of providing a tailor made diet. There are some useful links in the Home Cooking section and this thread
might be of use. The fresh food company Different Dog might be worth looking at. They have a vet on the staff and if you telephone them they will ask her to call you back.
Before you make any changes it would be best to discuss these with your vet. Is your dog on Denamarin or milk thistle supplement? If not, perhaps speak to your vet about it. Also worth looking at is Golden Paste (turmeric).