I am new to the backyard chicken phenomenon. We have 2 French Maran hens (Claudine & Oona), one of whom is having egg laying difficulties. Eggs are being laid without the shell by one of the hens. Occurs about every other day, no laying in between or an occasional full egg. Both hens are 6 months old and are on Layena crumble with oyster shell. We've also added straight oyster shell as a side dish. I've offered Greek yogurt, unflavored in hopes of providing immediate digestive calcium but doesn't seem to help. Oona continues with her shell problem. Both hens are cooped at night but have free run of the yard during the day, eating grass, bugs, etc. I bought them some fat night crawlers at the bait shop. Claudine loved them and gobbled them down; Oona seemed put off by them. Is there such a thing as a picky eater? What can I do to help Oona with her calcium deficiency and/or stop her laying until her body is fully equipped to do this?