Hello, usually this puffed up appearance with the head pulled down is a sign that she isn't feeling well. Unfortunately it could be many things.
Is she eating and drinking a normal amount for her? Going outside with everyone? Roosting at night? Laying normally? Have you found any egg matter in a nest box?
Also, if you haven't, pick her up and do a full exam, check around her vent area for mites/lice, check if her crop feels normal, feel around her abdomen etc. if you aren't sure what is normal, grab another hen and compare.
Let us know what you do or do not find.
Good luck!