Yes you are right. Do provide in calcium some way. Give oyster shells, give the egg shells (crumbled) back in a separate bowl, or if all the eggs have weak shells, give crumbled calcium tablets in there feed for a boost. But if the flock lays eggs with strong shells there is no reason to worry about calcium. One hen is not the flock.I agree with most of that but free ranging won't provide sufficient calcium to prolific layers unless there is a lot of limestone in the area. Otherwise, there isn't anything in normal forage that is high in calcium carbonate.