Hard to say. It could be as simple as the Austrolorp not eating the oyster shell. Or it could be a problem in her egg-laying sytem. Or it could be that for some reason she is not absorbing the calcium that she takes in.

If you can feed some high-calcium greens, that might help. Alfalfa is great if you can find some. I think also dandelion greens and clover, but you'd better run a google to check. Try something like: forage calcium chickens. You might also find something about this on Velvet Sparrow's website.

Here is a link that might be useful: Velvet's site - Bookmark it!

We occasionally have the same problem. We always have oyster shell available and the chickens free-range over acres of all sorts of healthy vegetation. If they won't eat the right stuff, I don't see how you make them do it. The problem never lasts long.

Thank you both for your answers.
I went to the Velvet Sparrow website and read that cooked eggs with the shells ground up can help restore calcium.
Since the dandelions, clover, etc. are rather hard to find right now with the heat, I think I'll try the eggs.
About 2 years ago, we had a pet leghorn, Betty,who roamed the back yard, while the other chickens were penned up. My neighbor told me she fed eggs to her songbirds and they liked them. I fed eggs to Betty almost every day and she loved them, but about a month later she became egg bound and was miserable. At that time, I blamed the eggs.
Now I wonder if I fed too many eggs to her and it affected the eggshells in some way. I think I will try an occasional cooked egg for all the chickens and see if it helps.
Again thanks for providing direction...I'll write back with the results....Lina.

A quality layer ration has adequate ca for laying hens but a container of crushed oyster shell is ok. Ground egg shells provide a more readily available Ca than oyster shell. Weather can effect the shell quality and the rate of lay. Age and genetics are also a factor in egg & shell quality; as mentioned in another post, the problem usually corrects itself.