The way she is behaving does sound like it could be related to senility. But I can't stop thinking that there is a connection to the 'coolness' of the countertop. It's my guess that she is nausceous and hot, so much so that she won't leave that countertop, even to pee. When you're nausceous, you don't want to walk, you don't want to be touched and you tend to want to be cool. I know I've already said that but it's just my hunch but hopefully your vet will help you really get to the bottom of this mystery. I can only imagine how hard this has been having to watch her be this way day in and day out without any resolution. Hang in there!