Need some help with a fairly new chicken who has a bald butt. As of yesterday, we didn't notice any feathers missing. We had a party last night and the kids were running around in the backyard, so not sure if she is stressed and perhaps plucked her bum? We use DE on the flock, so I don't think it's mites/parasites. I didn't notice any either. I've taken a picture - everything was fairly clean. We have four hens and at least one is pooping somewhat runny poop so I just added sulmet to their water today. I have noticed on occasion that there is a very soft egg in the nesting box. They have access to oyster shells and when I notice a soft egg, I give them eggs with egg shells. I felt the area and couldn't feel anything hard inside. The area is soft and squishy and it doesn't seem to bother her when I touch it. She is lower in the pecking order due to her and the other hen being new to the flock. There is occasional pecking, but usually just when treats are set out. Here is a picture of her behind. Should I be worried? Is there something I should be doing or checking for? Thanks so much for your help.