Buy a bottle of calcium citrate with vitamin D3 and keep it in the run or coop. I've been urging all chicken keepers to do this. Oyster shell (calcium carbonate) is fine for hens that are normally laying good quality eggs, as it will be absorbed by most and balances their need for calcium. And Tums calcium carbonate based antacid will work in a pinch, but calcium citrate is the easiest form of calcium to absorb.
The bottle of calcium citrate comes in handy when you have a hen suddenly show signs of reproductive distress as your hen has. The concentrated calcium will work on different levels to get a hen through a reproductive crisis and it will help to regulate the laying cycle to prevent chronic problems. This is not to be used long term, just in a reproductive crisis until its resolved.
I keep a flock of chickens aged new to very old. Old, retired layers often have reproductive issues, and I've learned a lot from dealing with them. In particular, an eleven-year old Wyandotte hen named Lilith who has never completely given up the notion she can still lay eggs and not expect it to turn into a disaster.
What I've learned is that if you see a collapsed egg hanging from the vent, there is often more material inside. Sometimes that "material" is an entire second egg. Releasing two eggs per egg cycle can happen to any aged hen, including new layers. What happens is there is usually not enough calcium in the shell gland for two eggs and one egg is shell-less. These are very difficult to pass and often collapse, causing a disastrous "traffic jam".
Giving a concentrated calcium tablet at the very first indication of trouble helps generate strong contractions to expel the backed up egg material. Continuing to give a calcium tablet each day until eggs return to normal quality will also help regulate the egg cycle to return it to just a single egg per cycle.
Keeping the calcium citrate on hand in the run means you can grab it fast, get the hen started on it fast, and get the problem resolved before any broken material begins to inflame the oviduct and cause infection that could kill the hen or render her sterile.
At the first sign of a fluffed up hen, tail held low and flat, perhaps a watery discharge running out of the vent, a calcium tablet can speed up the process of clearing the obstruction and getting a hen back to normal before the event does so much damage you end up having to euthanize.
If I see a hen has spent a couple of hours in a nest, straining, not producing anything, she immediately gets a calcium tablet. Often, that will do the trick, the contractions are strengthened, and out comes the egg. I've learned not to be surprised when it's followed by a shell-less egg. It happens more often than most people think. Two years ago, I had a "middle-aged" hen consistently plagued by two eggs each egg cycle. It took over a month of daily calcium citrate to get her cycle regulated to just one egg per cycle. She's been laying normally ever since.
