OMG, I'm so sorry. She beat the odds. It's rare for a cat to live that long, but there are a few even older. The average is only 12-14 years old. When you have a pet that long they're like a member of the family.
My last 2 cats were also a brother & sister of the same age & genetics. They passed away within a year of each other. So it was devastating to lose both in a year. Sigh. I just came across some pictures of them on a old disk yesterday afternoon. With the modern digital age we can take as many pictures as we want, & not have to wait for or pay for developing. I thought I had a lot of pictures of those cats, but these days since we even have cameras on the simplest mobile phones too, I find I already have more pix of the new cats, who will only be turning 3 y/o later this spring.
LOL, my sister takes tons of pix of her pets, & even pix of her food to post on Facebook.
My cats are either on me or laying against me most of time I'm sitting or laying around, & follow me wherever I walk most of the time. Right now the girl is in my lap, & the boy is right beside me. My old cats were the same way. I'm very attached to them. Before I got laid off, when I'd get home from work they would greet me at the door doing a happy dance, meowing & purring every day.
You may consider getting another pet someday. I've had pets all my life, so with none in the house, it got too quiet & boring. So for me, a home with nobody in it but me or no pets is incomplete.