These are three reasons to suspect shell gland issues. If feed has anything at all to do with it, it is how her body metabolizes calcium, since none of your other birds are affected, so I would carry on feeding what you're feeding and not mess with the other 3 birds' diet while trying to fix this one's issue, which probably has nothing to do with feed.Hi. My same little hen that seems to have all the problems is still having egg problems. Originally it was a bunch of calcium deposits, now, the past few days her eggs have been basically white (normally they are tan) and today I walked into the coop and her egg was broken, sitting next to another egg
You might find this useful
https://poultry.extension.org/articles/poultry-anatomy/avian-reproductive-female/