I would bring her inside to a basket or crate where it is warmer. Give her some water with electrolytes if you have some, and offer her some chopped scrambled egg. She may be sick or hurt, or dehydrated. Pull off any dried poo, and if needed you can trim excess feathers around her vent. A warm shallow bath when she is feeling better may help to clean her up. Feel of her crop to check if it is empty, full, firm or soft, or like a balloon. Look her over for lice and mites especially under her vent area. Feel of her breast bone to check for weight loss, since feathers can hide that. Look for any fullness in her lower belly. Has she recently been laying eggs? You can feel inside her vent an inch or 2 for a stuck egg, but you should feel nothing if she is not egg bound. Older hens can suffer from reproductive disorders such as internal laying or egg yolk peritonitis. Crop problems or worms can also be a problem.