I just went through a spell with my hens a for a few weeks. I'm hoping they're coming out of it now. I got several soft shell eggs and found a couple broken ones in the nest boxes and on the roosts. I had only found 2 in the previous 12 months. While this is happening, my egg production went from about 17-19 a day from 22 hens, to 6-8 for about 2 weeks. I had no idea what was going on, and I'm actually still not sure. Everyone looked fine, acted fine, ate and drank fine...and they get plenty of yogurt, goat milk and other calcium rich treats, they free range all day, and they have oyster shell free choice.
So, anyway, I was searching for what it might be the problem and found a thread on worms. I never suspected them, and still don't know if they had/have them. Like I said, there were no signs of that. I didn't really want to worm them since it said how hard it is on them, then I read about putting cayenne pepper in the feed for a natural worming treatment. It also said that pepper would jump start lagging egg laying. Skeptical, I tried it. I peppered the feed in the feeders until it looked a little "rusty".(just for 1 day) Then I peppered some rice (made with goat milk), and noodles for them. Nothing at first, but after doing it several days, production is going up, 15 eggs, 3 days in a row now, and not a soft one in the bunch. I peppered their feed again today, since it said to do it once, and then 10 days later, and so that's it for putting the cayenne in the feeder, but every other day I still plan on peppering a morning treat for them. Something made them start laying. I use black and cayenne on the treats.
Maybe you could try this for your hen...On the days off of the pepper, I give them some oatmeal (made with goat milk) yogurt and some apple sauce. Yep, spoiled, and ultimately, ruint chickens. lol Hope this helps.
Oh, and you can look it up on this sight, just search pepper and egg laying or natural worming, or low egg production...If you can't find it, and want it let me know, and I'll see if I can dig up the link.
Good luck!