I have been feeding my hens a mix of unmedicated chick starter feed (21%) and the layer mash (13%) so the protein content has been 17% for the past month. I still fed fermented grain at the rate of 10%. I added sunflower seeds and flaxseeds (linseed) to the commercial scratch grain which initially had a protein content of 11%, so the protein that the hens have been eating should still be over 16%.
They've always had access to crushed egg shells but I started offering feed-grade limestone powder mixed with a little salt free choice to make up for the low calcium content in the chick feed.
All of my hens have been laying slightly bigger eggs, however, the hen with the issue popped out two more fairy eggs after the change in diet and no normal sized eggs.
I suspect that she may be laying internally. Her abdomen is a lot bigger than it was 2 months ago. I thought that it may be weight gain as she was eating but not laying, then I realised that the production breeds often have reproductive issues even as early as a few months old.
She never laid everyday as would a production hen though, I have an indigenous hen that's younger than her that "outlayed" her.
She seems completely normal at the moment and if I didn't know which egg belongs to which hen in my flock, I wouldn't have known anything is wrong with her.
However, I do know that a decline in her health is inevitable. I won't be getting any sex-linked production breeds again