Sounds serious. Have there been other symptoms?
No shells is not common at all.
Sometimes there is no remedy.
If the bird is a pet or valuable, here's a few things to try.
Calcium, phosphorus, vitamin D3 and magnesium should be in the correct ratio.
First, cut out all treats, scratch and supplements except to provide oyster shell in a separate container in a conspicuous place so she can find it. Just don't mix it with feed or that will cause a fault in the correct ratio which can also cause shell issues.
If not, I'd try a reboot. This is only a suggestion but could work.
Put her in a dark place except for about 6-8 hours of light a day to increase the melatonin. That will reduce the hormones inducing reproduction. Within a week, she should stop laying.
Keep her on short days with a grower ration to try to get her body to regulate itself. Wouldn't hurt to give some probiotics as well. That could be some plain yogurt with active cultures or an avian probiotic powder. I use Gro2Max.
After a couple weeks of no eggs, go back to layer feed and simultaneously start increasing day length about 15 minutes a day.
It doesn't happen often but possibly there are mistakes in feed formulation. Usually because a valve malfunctioned or a blockage in an ingredient. Excess salt or some other nutrient issue could be the problem but it is very unlikely.
More likely is a problem with the shell gland which could be genetic or disease related.
Also try a bit of raw apple cider vinegar in the water - perhaps a Tbsp per gallon.
That can help them absorb calcium.
Good luck.
