Soiled Black Wet Butt

Two things--she might just have a poopy butt, either do to drinking lots of water and having too much fluff. You can trim it off once a month, clean her up, and give her yogurt twice a week and apple cider vinegar 1/2 oz per gallon of water. Secondly she may have vent gleet, a fungal infection that smells bad and causes oozing white material and redness around the vent (think yeast infection.) Treatment is the same as above plus mycostatin or other antifungal cream, or Nustock a cream from the feedstore applied daily.

 

I doubt it but some sites say that it can spread by the rooster. Check her crop in the morning for sour crop (full squishy balloon-like.) Could she have coccidiosis? Symptoms are lethargy, ruffled feathers, puffing up with tail down, and diarrhea (sometimes bloody.) Treatment would be Corid (amprollium,) a cattle med, 2 tsp liquid or 1 tsp powder to 1 gallon of water for 5-7 days. Older hens can get it if they are new to the land where new stains are present, or when a new strain is brought in by new chickens or on the shoes.

 

An anti fungal cream, like Monistat, would probably work very well.
Vent gleet is basically a yeast infection.

 

Plain unsweetened yogurt, maybe some extra protein like eggs, and just her chicken feed. Don't feed too many treats like scratch.