I agree. I always tell parents that crying on the potty is unhealthy and I won't put a kid on if they're fighting it. It can lead to esteem issues that compound the potty training process, and can also signal the beginning of a power struggle. In my opinion it's best to wait until they are more ready.

I'd try focusing on the kids in care who wear underwear and giving them praise, reading stories about using the potty and hope that she gets a more positive view of it. You can also start making diaper changes less fun (if it is fun now). Just have a neutral expression and say very little during changes. Not give the cold shoulder, but just don't give any more attention that is necessary. You didn't mention how old, but I assume it's not a lateness issue. Some kids take longer than others, you don't want to get off on the wrong foot.