“Potty trained” DCG not making it to potty

I’ve been looking after a 2.5 year old girl for a couple months. Her mom tells me she always makes it to the potty at home, but here she doesn’t always make it. Even when she tells me she has to go, she sometimes pees in her pants just as she gets there. Some days it’s more often, and other days she always makes it.

She’s only been potty trained very recently, I guess she caught onto the potty really quickly and tells someone when she needs to go, or just goes to it herself with an announcement. She never wants to sit on it when I suggest it, for example before we go outside. She wears panties, but i have pullups here from when she started and she was still napping - which she stopped doing after the first couple of weeks.

Should I just leave her in panties (She has extra clothes here), suggest pullups to her mom while shes here, or what? I’ve kept her mom in the loop, and she doesn’t seem concerned, or is at least not telling me if she is.

Any suggestions?

Leave her in panties. If you switch to training pants or pull up pants, she doesn't get the trickle of pee running down her leg to remind her to run and you won't be able to see that she's had an accident because the training pants/pull ups absorb that, so there's no visual clue she's wet for you.

I would have set times where you send her if she's not been lately. i.e just before you go outside, expect all children to pee or at least go and try, same for lunchtime or whenever. That way, she's not singled out but where she's resistant, it's not an option but to go and try.

If she's newly toilet trained and everything you say suggests that's true, just tell her (not ask her) to go if she's not been in there for a while.

Thank you! I really appreciate your advice!