Yes, my RB Starr did this the last few months before I let him go to the bridge. He just became very lethargic and some times he didn't even want to eat. He was also very over weight because of the pred he had to be on. I really think that the pred is what caused his decline in health. He would poop and pee every day though.

I'm really surprised that your vet isn't more concerned about your cats eliminating habits. I've never heard of such a thing. I do know all cats won't poop every day but all of mine seem to do this. Have you had her heart checked out?