Dog peeing in the house at night ONLY when specific person is home?

So for some background context -- I (in my 20s) live in the basement apartment of my mother and her partner's house. When they go away (which they do fairly often, either to travel or to visit my grandmother), I look after the dogs. There are two dogs, both seniors -- one is about 10 and the other is about 14. The 10 y/o has recently started peeing in the house regularly, almost every single night. It's definitely her, because it's consistent even when the other dog is in the basement (he can't get upstairs by himself).

The thing is, she only does this when my mother is home. If she goes away and her partner is here, there's a chance of pee but it's rare. And if it's just me it almost never happens -- the last couple of times I've looked after them there was only one accident, which happened when I was sick and slept in longer than usual so it was likely just an issue of her not getting out as early as usual in the morning.

I've had dogs my whole life, as has everyone else in the house, and we're all pretty perplexed with this. My mom loves this dog, and the dog loves her -- she gets mega excited when she comes home from being away. The first time she did this was actually after she got back from a trip, which made us think it was because she was upset, but it's now become a consistent enough thing that my mother has to put pee pads down every night because it's more or less guaranteed the dog will pee in the house. She doesn't do anything to alert anyone she needs out, and when it's just me here she doesn't go out any more or less, since we're all on roughly the same schedule.

Any ideas as to what's causing this?