Sorry about this hen. I would make sure she’s in a cozy safe place and find a way to keep her upright… either supported with towels or try some spurts in a chicken sling. Make sure she has feed and water within reach.
You are going to need to examine this hen. Check her carefully for injuries and gently palpate her legs and feet. Feel her crop (food pouch on chest) and check if she has a sharp, pronounced keel bone (breast bone). Look at her vent. Is it clean and not puckering? Feel her abdomen (fluffy area between and behind legs). Does it seem bloated? If you can’t tell, compare her to one of your other chickens.
when did she last lay an egg? Is she open beak breathing?