Very sorry for your loss. Our animal companions become such a vital part of our lives that there is a huge void when they leave. I am a cat owner for the first time in my life after rescuing a kitten downtown earlier this year and now I can't believe what a great pet she is.
The most important thing is that you gave her a great life, not all cats are that lucky. 20 years is like a human living to 100. And healthy almost to the end, from the sound of it. Bravo to your family. Here is mine, estimated to be about one year old: