I have an Easter egger that lays very thin-shelled eggs, and has since I got her from another chicken keeper in my town. The other hens I got from her lay regular hard-shelled eggs. I have always fed my chickens Purina Flock Raiser with free-choice oyster shell, without problems. After this hen’s eggs did not improve I switched to Layer feed, first without free choice oyster shell, and now have added it back. Still no results. The other hens crack her eggs when they lay in the same box. Any other remedies before I have to cull her?