It does sound like the Rimadyl was inappropriately prescribed. There are others thought to be kinder to the liver, but any of those nsaids can cause the same effects. They should be accompanied with liver support.
Since there are elevated liver ensymes, I would add liver upport now. My favorite is Country Life's "Liver Support Factors".
Slippery Elm Bark is very healing for the digestive tract, as is l-glutamine.