I have a hen that has that posture, and she does not lay. I feel like she has a reproductive disorder, such as internal laying. Her eggs used to have a soft end that frequently broke easily. Your hen’s vent needs bathing to get the poo off. Then after she dries, try taking another picture of her vent. It looks like she has had diarrhea for a bit, and it has caked. It may be irritating her skin, or she could well have vent gleet. That is a fungal disease, but hard to tell. Is she molting or have her tail feathers perhaps been pulled out by the others?