Thanks for the suggestions! Soaking her bum in some warm water for a few and then gently wiping (and wiping, and wiping) with a warm washcloth was enough to get her clean!
I just got my first set of chicks on Tuesday - 8 baby Buffs. They're all looking great except for one which has the following condition below. This looks like it's right on her rear. What am I looking at? My wife and I have taken a warm wash cloth to it with no avail. It's quite hard and...