Can old cats (or dogs I guess) suffer from dementia?

I have a 15 year old cat, Smokie. She’s gone deaf. : ( And in the last month or so she’s taking to going upstairs and yowling. It’s the sound a Tom makes when they’re in heat, or the sound a mother cat makes when she’s calling her babies. Smokes had one litter many moons ago, then I got her spayed. Rick went up there once when she was doing it, and she was sitting on a couch that I’d had all of her life, until we bought new ones three years ago. She was sitting there, facing the back of the couch and just yowling.
Well, some of you may remember that I had another cat, Emo, who we’d had for about three years who was run over by a car and died. Smokey and Emo were far from being friends. Smokey doesn’t like ANYBODY but Rick and me, but Smokes started this yowling thing about a week after Emo died. And that’s another thing. Her personality is changing too. She’s becoming much more friendly with people, even strangers, and that is NOT like her…..any thoughts?