Oh Valerie, so sorry to hear about your loss
Big Hugs!
Cats are very good in hiding their symptoms. She might have been sick without you noticing. One of my cats was absolutely fine (so we thought) when I just by accident walked through the laundry when he tried to do his business ( I mean.. seriously, you really wouldn't see that or specifically watch for it, right?). Well, I noticed that he had some trouble and took him to the vet. He said, oh yeah, constipation, some tom cats get that, no problem, you can pick him up again this afternoon. A few hours later I got a call... our sweet Gizmo was already so weakened that he didn't survive the procedure