cleaned up, then what about parasites. I have heard about mites that center around the vent and with this particular case the hen stopped moving. She got real sick and wouldn't eat or anything.
She was removed from the flock and given a warm bath and a very good blow dry (important to get her completely dry) and she will love both. check for problems at the base of her feathers where the quil comes out of the skin. If it is mites put some DE or what ever you use to treat for mites on her and time to get better if that is the problem. I hope it is as easy as that but am learning myself.
If she has mites the rest need to be treated too...
Depending on where you live and the weather these may not be available (ground frozen/snow covered).
Does she have access to grit(Course sand & small pebbles)?
Oystershell?
Try Organic Apple Cider Vinegar in her water, 1 teaspoon per/Quart (glass or plastic container only). It helps digestion.....eletrolytes in her water the next day, give 2-4 drops PolyViSol (non Iron) daily.
if the crop doesn't empty you can add a little olive oil to yogurt.
I had the same issue with a bantam just 2 weeks after i first got chickens, it took me a while to notice as i was not an expert on their behavior.
The pics look exactly like the vent on my now deceased bantam. Follow the above advice, bring her inside, but additionally massage the crop, try to ensure you dont push the food upwards (Chickens dont have a wind pipe and food pipe, it is all one) massaging it will help break up the food in there and help her start digesting. (At the moment, if she has an impacted crop she is slowly starving herself to death, her energy levels will be low and you need to try and keep her hydrated as much as possible)) i was advised to buy a tiny turkey baster and give the chicken olive oil and very diuted apple cider vinegar. Make sure that all your other hens have access to oyster shell and grit, Chickens do not have teeth and the grit and shell act as teeth in their crop to aid the break down of food. If their coop has straw, you may want to over time replace with wood shavings, the chickens will peck and eat some of the straw and they find it hard to digest.
You are likely to have to pay a fairly large amount of attention to help her pull through, but it is well worth it. Make sure even when the chicken appears to be better, keep up the routine maybe 1 or 2 more days than you would think to make sure you "complete" the medicine!
Alas i was far too late to save mine, hopefully you have caught yours soon enough and can learn from my experience, good luck!