I'm so sorry. We had to put down our family dog a few months ago as well. It was very sudden. She was a champ, and didn't show any signs of illness until it was far too late to save her. I still get hit with waves of sadness when I think about her, or go to my parents' house and realize she's *really* not there anymore. 

That said, I'm sure she lived a full, happy life with you and the family. It just hurts to know that doing the right thing means losing something you love so very much.