If her being with you part time now is a new thing I'm sure it can be confusing or she can forget to ask you to go potty (different caregivers, different expectations). Who knows, with mom being home with her she may get more reminders etc just due to the fact that mom only has the 2 of them. It sounds like she is too busy having fun and is forgetting to go.

I disagree that kids that are trained won't pee in pull-ups. My daughter is 100% trained and has been for over a yr now. If she has ever been placed in a pull up (really long car rides "just in case") she will choose to pee in it out of laziness and won't even ask to go to the potty (she still wears them at nap/night). I actually found pull ups super confusing for her when we started training as she would just go pee in them and treat them like a diaper. She doesn't wear them for long car rides anymore and tells us she has to pee and we pull over.