She may have a broken egg inside her and that's causing her to strain to try to expel the remains. Just this past month I had a chicken with the same problem. There was evidence in her case that a soft egg had ruptured inside her, so I gave her some calcium supplement to begin with.
I also started her on penicillin since bacterial infection in the broken yolk is a foregone conclusion. Then I tackled her prolapse, which also had a pecking injury and was bleeding.
I bathed her in warm Epsom salts. Then I dried her off and sprayed Vetericyn on the entire vent area and prolapse. After than I wet a cloth with witch hazel and held it to the prolapse. It's an astringent. Then I used cortisone cream on the tissue and gently pushed it back inside.
I kept her in a crate indoors at night so she wouldn't get pecked again before her prolapse began to stay in. I let her stay outside in the run during the day where she could see the others, but she was in a protective pen. Several times a day I would wet a cloth with witch hazel and hold it to her prolapse for a minute, then smeared cortisone cream on it one time and the next time I alternated with Preparation H. and pushed the prolapse back in.
Patience is necessary when treating a prolapse until it finally decides to remain inside. I continued the calcium supplement all this time as it's important in getting the egg remains out. It took my hen six days to pass the remainder of her ruptured egg and then the prolapse stayed in after that. I didn't let her back in with the others until I was absolutely certain it would remain in where it belonged.
