
YOu did the right thing, its not fair to let a dog suffer like that. I think everyone who has to have a dog PTS always questions "was it right" after, I know we did. Just remind yourself, would you like to walk in circles, not eating but still have lived to a good old age. It is natural to feel upset and your gran I asum had her dog for 16 years, thats a very strong bond that is built in those years. Its like loosing a family member to some people.
I'm sure you did do the best thing for the dog and your gran in the long run.
take care