I cant remember when DS went to 1 sleep - i think it was around 18 months.... (he has been such a bad night sleeper that he needed his sleeps in the day..). what do the carers think? they must see that she is struggling with the 1 sleep...
Maybe they could allow her to have 2 sleeps (even in the baby room) for a little longer, esp as she has been unwell. I know at DS1 creche they have a couple of kids that have done that for a month or so while they transition. or you could get the schedule of what they do and try to follow that at home too - it may take a while but she may adjust ok? i did this when DS1 went to creche (he has been at FDC beforehand and much more free with time etc) and it helped. you may find she needs an earlier bed time perhaps?
I would speak to the room leader and maybe the director to see what they think you should do - maybe when she is settled in the room it will be better - i see most of the kids want to do what tje others are doing...