I know exactly how you feel, I had to take our sixteen year old puss on her final trip to the vet two years ago, and her eighteen + sister died earlier this year. As you said, you can get a lot of comfort in remembering what a good life she had. I was really upset and started helping out at a cat rescue centre, and in the end couldn't resist taking home a lovely black and white cat that had been there six months, and who has made herself very much at home. Condolences and remember that you always did the best for her.