KJS--
This is so sad. It just breaks my heart to hear your pain...
But yes, I think you did the right thing. Yes, she looked all cute and attentive at that moment--but you know very well that so much of surgery depends upon the recovery period..and it sounds like there was not much chance of a good recovery. If she was too weak to get herself around on three legs and you had to carry her back and forth to eat and go outside...well, that poor little dog was going to end up suffering...and may have been put down anyway after all that. You did the right thing.
((((hugs))) and sympathy...