It is so hard to watch. The best we can do is make them as comfortable as possible and helping them enjoy each day. I had to do the same for Melody and Mardi to help them walk.
Check with your vet, but my vet had Potion, who did have altered liver values after taking Rimadyl, on Hepagen C (milk thistle) and wild salmon oil. They both help support liver function.
Sending mojo and gentle hugs.