I find hearing kids cry one of the hardest things in the world to do. But in a multi-child care situation, it is IMPERATIVE that everyone gets the rest that they require. Yes, when she is at home with Mummy, she can have a shorter nap, and then if she is cranky Mummy just snuggles/caters. This DOES NOT fly at daycare.
So I would suggest strongly to Mom that it is easiest if the routine is the same at home and daycare. But from your end, I would just leave her the full 2 hours (or whatever your minimum is). I have had noisy nappers, and almost without fail, they figure out that I am not coming for them until quiet time is over. Even though at home, they "only nap for an hour or so".