Is she back on her eggs now? I would not give up hope. I had the same thing happen because my hen went back to the wrong nest. I thought all of her eggs died. It happened around day 7 for us. Well they hatched this past Friday! So they still could hatch. I would wait and see. Is she back on the nest now? As far as placing a chick under her I have done that twice successfully. You have to do it as closely to the chick hatching as possible for the chick to imprint and the mother to accept. Just slide it up under her and just watch to make sure she accepts it.