She can eat what the others eat (all-flock is good for all your birds) and all the laying hens will help themselves to oyster shell if it is available. But you can give this one a calcium +D3 tablet once a day for 5 to 7 days to help her out. Citracal or a generic equivalent will do and you can get it any place that sells vitamins or supplements. Easiest to administer at night after she has roosted. Just pull down on her wattles or the skin below her beak and when she opens her beak just pop it in. When she closes her beak she will swallow it no problem. The tablet will look large to you but don't worry, she can swallow it, a chicken can swallow a whole mouse.Sorry I replied to you somewhere else I know which one she is I will try this but do I need to separate her? Or can I just feed her away from the others once a day?