Soft shelled eggs from one hen in a flock of six

[trudle]

I have a white leghorn, about eighteen months old, that was rescued from an abandoned egg factory. When I first got her, she was very weak, so I kept her separate from my other chickens and gave her lots of oyster shell as a calcium supplement. She started laying beautiful eggs, almost one a day. Then, when I put her in with the main flock, I could not put so much of the oyster shell in the regular feeder. She has started laying soft eggs, and only one or two a week. I wonder if, as a chicken bred for factory laying, she has just reached the age when she will stop producing eggs, or if there is something I can try to boost her calcium to see if she can get back on track, while at the same time keeping her in the coop and pen with the other five birds. Suggestions welcome!