Hopefully as a senior kitty she's been going to the vet regularly and been having her blood parameters checked for any signs of problems with her internal organs (remember, well pets visit vets too!). Sometimes in older cats they can have acute issues with their livers and kidneys, although chronic degeneration is more likely. With those diseases however, you are more likely to see your cat eat less, drink and urinate more and be more lethargic. So I wouldn't get too worried about those as being a reason for her change in behavior.

If you are really worried though, it never hurts to have your vet take a quick look and listen to your concerns! There are many internal problems that can manifest as behavioral changes and your vet is there to address your concerns about your kitty, whether further testing is warranted or not