Well I have some interesting news. I have had to keep the girls locked up in the run for the last several of weeks. No Free Range at all, do to an unrelated predated issue that still has not been resolved.
And well I have not had a thin shelled egg in two weeks now. Her eggs have steadily gotten better, and now they are pretty solid. So I am wondering if she was getting what she needed from the free ranging and she was not eating enough of the layer feed. Now that she has no choice, but to eat the feed, she is getting the calcium she needs.
I guess that is one plus for keeping them in jail.
Interesting observation.
It would seem that may be the case if she is now just eating layer feed, oyster shell on the side and the goodies that you give them.
She may have not been consuming enough calcium.
Just a thought...What you may want to do if you decide to free range/let them out when the predator issue is resolved, let them out later in the day-say a half-hour to hour or so before roosting time, this way the bulk of their (her) diet would be the layer feed during the most of the day. See if she still stays the same with harder shell eggs, if so then you can start possibly increasing the time they are out.
Glad you are seeing improvement.