My hens are molting and I noticed that one girl has what looks like a swollen/puffy area that is a little red on her butt area. I think it might be the top part of her vent, but I'm not sure since I was in an awkward position. She's acting normal. It isn't hard and I saw her poop (which looked normal). What is this? I'll also try to look at it while she's roosting, I should be in a better position then.