My older cat’s new obsession with sitting in the bathroom sink has me baffled

I have a 12-year-old tabby who’s always been pretty chill, but lately she’s developed this weird habit of jumping into the bathroom sink and just sitting there for ages. It started a couple of weeks ago, and I thought maybe it was just because it’s a cool spot during this heatwave, but the bathroom isn’t even that warm or cold. I’ve tried blocking the sink, but she finds a way in every time. She doesn’t seem distressed or sick, and she’s eating and using the litter box normally. It’s just the sink thing that’s new and a bit puzzling. I’m curious if this could be some kind of comfort spot for her, or maybe she’s marking territory? I don’t want to discourage her if it’s harmless, but it’s also kind of inconvenient since I use that sink daily. Has anyone else had an older cat suddenly fixate on a strange spot like this? Should I be worried about any underlying health or behavioral issues? And what are some gentle ways to redirect her without stressing her out?