I would be curious as to what happened and ask about it. Not in a "you broke it you pay for it" way but more out of curiosity. From your description it sounds as if it has been bouncing down the stairs. It is hard to miss a thing like this. Who knew but didn't tell?
It would be stupid if you felt angry with the parents if they know nothing of the incident and it might be a good thing to let the daughter know that it is not ok to break something and just walk away from it.