I have heard a lot of old lore about animals and reacting to a human's estrus. I used to have horses and old timers swear that stallions can sense it on a female rider. It's not too delicate a subject to reply to. I had a cat who would pee in odd and unusual places when her heats were come due, but that stopped when I had her spayed, thankfully. I don't think cats are as scent driven as some other animals, and I honestly don't know the answer. I would not say it's beyond reason to think she is picking up some sort of hormonal flag, but were it that it would be more instinctual than behavioural.

I would be more inclined to say it's due to some type of stress. It could be due to the type of linens, or the odor of your bedding. Is the kotatsu covering made of the same material?
I think you need to look her total environment and try to determine what's upsetting her. Have you changed or washed the bedding shortly before she pees on it? Have you recently changed the brands of litter, or tried adding another box with a different brand of litter? Is there another cat living next dor?

When was her last checkup?

Here is a link that might be useful: Outside the box