I think that she was probably vent pecked by the other chickens, possibly because she might have had a prolapse. Her abdominal contents, possibly intestines, look to be exposed. Hopefully, the abdominal wall is still intact. Either way, her vent or cloaca was damaged, and there is some infection. I would give her one or two shallow soaks each day in warm water. You could add a little salt to make saline or use some Hibiclens or betadine in the water to help fight infection. Epsom salts also works. When she is drying, apply a little plain Triple Antibiotic Ointment. This may take some time to heal, but try to keep it clean. She may die from infection if the abdominal wall is pierced, or she could herniate. She needs to be kept away from flies, since maggots would kill her. I hate to separate chickens since it is hard to get them back into the flock later. But she needs to be separated while she is healing. You could let her visit the flock each day with supervision, just so they remember her. I hope that she can survive this. Let us know how she gets along.