Check her crop now, to tell us if it feels full and hard, puffy like a balloon, or is empty. Fluid could be a sour or slowing crop. First thing in the morning check to see if it has emptied ( before she eats or drinks.) When you gently press on her crop, smell her breath for a sour or bad odor. What are her poops looking like?
Can you get her drinking some electrolyte water, or add 1/2 tsp of sugar to some water, and give to her. Has she been eating? What do you feed? Do you have granite poultry grit available? Has she been wormed recently? Check her for any lice or mites under her belly and elsewhere.
Hens over 2 can have cancer, reproductive infections, and can suffer from impacted and sour crop.