How old is she?
What type of food/treats do you feed?
Any signs of respiratory illness -coughing sneezing, runny nose/eyes?
Do you offer oyster shell free choice?
Any signs of lice/mites?
It could be due to a nutritional deficiency, lack of calcium and vitamins E, B12 and D as well as phosphorous and selenium or illness/disease. If she is an older hen, it could be signs of internal laying/reproductive disorder like Peritonitis, Salpingitis, tumors or cancer.