We noticed this when feeding the chicks never seen it beforr. Though to me it looks like the rectum poped out could it be or is something else simpler hopeing
Red thing on rectum
Looks like a prolapse. Ideally give her a soak in a warm epsom salt bath and gently wash the area well to remove any poop. Gently push the prolapse back in, you can apply some hemorrhoid cream or honey to help reduce the swelling.
Here is more detailed information and pictures on how to treat: