Elder cat pooping in my mom's room and I don't know why.

Okay, so I have an old cat (19 F) who's been going into my mom's room as of late, and on a few occasions has pooped in there. It's just really odd because this isn't the first time this has happened. She'll usually do this for a week or two then stop for months and it repeats. She knows my mom doesn't want here in there to the point that even if she's going in there to rest, the moment she sees me she'll leave without issue.

I don't think it's feline dementia like my family has both jokingly and seriously suggested as she doesn't really show any symptoms relating to it, she can still get in and out of the litterbox just fine (she even used it some time before the poop was discovered), she she doesn't show discomfort using the cat litter (we even changed brands for the first time in years and she seems to enjoy the new one even more), none of our other cats have bothered her, and to my knowledge she doesn't have any negative feelings towards my mom. If anything it's the opposite since whenever she comes by my room she'll pop up and run to the end of my bed to get her attention so she'll pet her.

This behavior started some time a year and a half ago after one of our cats died, and said cat being one of her children. He'd done the same thing, but because he was legitimately dying and was sick and had only started roughly less than weeks before his passing. Any ideas to get her to stop? There's no signs of discomfort or sickness or anything of the sorts, she's even been caught once in the last about to pop a squat and immediately went to use the box without issue.