If she were mine first thing I would do is put her in a bowl in the incubator to limit movement. I would be inclined to take some dental floss and tie off the prolapse as close to her belly as possible and then a little later snip off what is prolapsed. It really does look to be only yolk sac involved. Do not do that yet though, hopefully others would have more advise in the emergencies section.Idk what happened, I noticed what appeared to be dried on poop. So, i got a warm damp balled up Kleenex and held it on wiping gently, no progress so I set it down beside me and looked up to see where Brownie was and then I looked down to see the chick run to Brownie but there was blood. I scooped it up its clearly tissue hanging. All of this happened in the space of two minutes.