It happens. Your flock will be upset for a few days...they really do grieve a loss, sometimes worse than others. Just make sure everyone is eating and drinking okay and reassure them the coop is safe.
It could also be one of those things where she just died. Sometimes they just die without exhibiting symptoms and other times they are ill and we just do not see it. They hide illness very well until it is really bad usually.
Sorry for you loss.