Is she going through a molt at all?
Any lice/mites?
If she *should* be laying but has suddenly stopped and she's not in molt, etc., then she may be having trouble expelling an egg or possible she's having some other problem like cancer, tumors, Salpingitis, etc.
If she should have laid and...
When was her last egg?
Do you note any swelling, bloat or fluid in the abdomen below the vent between her legs?
Is her crop emptying overnight?
Photos of her and her poop may be helpful.
I'd offer her some electrolytes, see that she's eating o.k.
If possible, get a fecal float to rule out...