Help, Lethargic Chicken with Red/Warm/Molting Patch Below Vent

[cachetona13]

Hello, just wondering how it went with your hen? I looked at the first video last night as I am thinking I am dealing with something similar. I am a little afraid of poking her with a needle, but starting to consider it. Mine has good times thru the day where she is walking around and pecking and was eating, but today she is less active and is eating less. put a bowl of her food missed with really fine powder egg shells and moist with some apple cider vinegar. fed her 1-2 tablespoons of yogurt yesterday and 1 today.
I am so concern, the photo is after she came out of the bath