If you know which one it is, try giving her a human calcium citrate tablet with vitamin D 3 tablet orally daily for the next 7 days. Tums or other calcium would work until you get the generic tablet. She might have a problem with her shell gland, but this will rule out a calcium deficiency.Are you using an all flock feed, not a layer feed? Layer has 4 times the amount of calcium in it than all flock. It is better to put crushed oyster shell in a separate container than feed. That way each hen takes it is she needs it.