Nap time inconsistency

So I work 5 days a week during those days my 18 month old goes to my mums for the day and I get how around 2:30 ish. When I have my daughter or my partner does she has her nap around 11ish maybe later the very earliest would be 10:30. This is a perfect nap time for us and she happily goes to bed around 7-7:30. When my mum has her which is the majority of the time she has her nap at 9:30 sometimes earlier. She dropped her 2nd nap a while back now. She is up far too long before bed time and wakes at 5 am because she goes to sleep around 6:30. No matter how many times I tell my mum to push the nap back she doesn’t and it’s killing me 😭