All pain medications, especially those used repetitively, bear a risk for cats. Metacam causes acute renal failure, not chronic. If your girl was diagnosed with chronic, she likely suffered from other problems with was only worsened by metacam. For the record, though, it is clearly stated on the label of ORAL metacam that it's only FDA approved for use in dogs. To be fair, however, there's a risk with practically any pain medication in cats, although I personally have NEVER seen a poor reaction from a young cat post-op with a pain injection.
I'll be truthful, if my cat were undergoing surgery, I'd opt for post-op buprenex (IM, for longer lasting effect) and would go home with oral buprenex. It's more expensive, but the risks to internal organs (liver and kidneys) is lessened.
As a side note, Mews2much, have you contacted the manufacturer? Boehringer Ingelheim almost always contributes to refund (or at least contribute) owners who've suffered ill-effects from Metacam.
I'm glad everything went well for Ripley!