If she's laying shelless eggs when she lays an egg, as WR says, it's highly likely she has a calcium deficiency.
I have a couple of very old hens, aged seven years, who insisted on laying regularly last season. However, I was wishing they would stop since every egg was shelless. Then I learned that you can give hens like ours people calcium, Caltrate or the store brand. This formula has calcium and the correct minerals to help a hen absorb the calcium.
The dose is one half a tablet each day until she lays solid-shell eggs. Going beyond that could start damaging the kidneys, can cause brittle bones, and may interfere with the ability to pass the egg easily, so it's important not to overdo it. This calcium therapy is strictly for hens who are laying soft shelled eggs, not layers who are laying normal eggs, and it does not replace oyster shell as the best way for layers to get calcium. I cut the half tab in half again so it's easy to swallow and I embed the pieces in a dab of peanut butter.
I gave the calcium at night as the hens roosted, (night is when the shell gland does its work) and they came to expect their "treat" and lined up at the door for it. It worked wonders. Their eggs were nice and hard, and I was able to sell them instead of feeding them back to the flock.
