It appears to be prolapse of her vent. It's when the tissue inside is protruding outside of the vent. Since it's been going on for so long, I'm sure it's suffered quite a bit of damage, both environmental and from other chickens pecking at it. I'm very surprised she's able to lay eggs.
At this stage, it has likely lost all muscle tone and flexibility, and is also dried out and tissue may be dying. I would doubt that it can be returned to normal. Usually, if you catch this when it first begins, keep it moist and cleansed to prevent bacterial infection and use cortisone cream on it to reduce swelling, it can be coaxed back in where it may remain.
Probably laying eggs is only going to make it worse. Does she have an acrid bad smelling discharge dripping constantly?