For mites or lice permethrin 5-10% spray or garden dust are used to treat, and repeat in 7 days for mites, in 10 days for lice. Lice will leave white clumps of egg at the base of feathers. The other chickens and the coop will require treatment as well. Empty the bedding and replace with clean. Where exactly on her body is the yellow thick scab--on the belly, chest, or under the vent? A yellow patch on the skin may be thickened skin from irritation or from pecking. Lying on the floor in wet bedding could cause this also. It is hard to see clearly the area around her vent. Vent gleet from a fungal infection of the digestive tract, may cause red, angry skin with white or yellowish patches. I would stick to giving her plain water with electrolytes and vitamins, and taking plenty of fluids is more important than eating at first. Offer probiotic plain yogurt daily. Nustock, a sulfur/pine oil/ mineral oil mixture found at feed stores would be could to put on the thick patch or irritated area around the vent. Is she having diarrhea?
