Glad that it is not a prolapse. You may want to separate the feather picker/bully into her own crate or similar with food and water, where it might lower her standing in the pecking order. Many try different approaches to this problem, such as flock blocks, swings in the run, throwing some scratch grains into the bedding to look for, tree stumps and other things to climb on, but just getting outside to roam is probably the best. As I say that, my girls are refusing to go out in our fresh coat of snow today. I will shovel an area for them to explore so they don't get their feet cold. Vent pecking can lead to cannibalism and death, so you may want to read a few threads for ideas. I once had a few wyandottes from the same hatchery, and they were bullies, so they went elsewhere. Just spend some time with them, and watch their behavior--it's also fun and you sometimes pick up things you didn't notice before. Here are a few threads with suggestions that may help:
https://www.backyardchickens.com/t/98165/what-i-am-learning-about-feather-picking-and-cannibalism
https://www.backyardchickens.com/t/1104846/feather-picking
https://www.backyardchickens.com/t/...ers-nothing-will-stop-them-brief-update-and-1