DD is 3 1/2 and been potty trained for a couple of months (except nighttime and naps). She is very slow to warm and doesn't like change much so it takes us a while to transition. She is also uncomfortable verbalizing that she has to go potty to anyone (including me), except her teachers at school.

She usually spends the day with her grandparents once a week (without me). When she first started potty training she would sit on the potty and pee at their house without issue. Now she is holding it even when she sits for 5-10 minutes and usually waits for a diaper at nap time and goes in it instead to pee. Or she holds it all day and goes when she comes home!

Now that you have background, here is my dilemma. She has been waking up dry at nap time for a while now so I was going to transition her to big girl undies at home, but I don't know what to do about the grandparents house given how uncomfortable she is at their house without me now. Do I keep having them put her in a diaper at their house for nap time and make the transition at home until she starts to get more confident? She is a sensitive kid and I want to be sensitive, but I am confused. WWYD?