Have you had any luck finding the vent opening to try and manipulate the egg out? Overly large eggs can cause egg binding and sometimes a proolapse will occur. Egg binding can be caused by a lack of calcium, dehydration, too large of an egg, young pullets laying too early before their muscles can work properly, and other causes. Be sure to keep the prolapsed red tissue lubricated and kept from drying out. Honey is good, and you may use other mild oils or hydrocortisone cream. Once the egg is retrieved, you will want to push the prolapse back inside.