Wow!! Ok I have a 12 month old that sleeps 2-3 times a day with an early bedtime. She gets 3-5 hours of nap time daily plus bed at 7:30. These parents are probably not even realizing thier child is over tired and there for not going to bed well.
I'd let the child sleep and act as if you woke her up, let it go a while then ask how bed time is going? If parent is still having challenges, show you are concerned and simply say...could she be over tired or maybe missing her parents etc etc offer solutions. Keep up the good work, don't let parents make your rules.