When dealing with these types of parents I find you have two options:
1- schedule a meeting after daycare hours and sit to talk. I believe talking with the parents is important.... only to try to work together, not to change your protocol or ways.... but to maximise the child's success
2- demand diapers or pull ups and do not accept the child for care until you have them, simply say that you do not find she is ready and that you will let them know when this changes
Option two is hard but the reality of i...t if they do not want to respect you enough to discuss the situation and options that you might suggest that they try at home.
Parents often think that we could do the potty training and that we are available to bring kids to the bathroom on a timer.... but that is not our reality and I feel we have to make this very clear to them.