Oops sorry I promised to update this thread and then never did!
Unfortunately, we made the difficult decision to dispatch her a few weeks after I made this post. I separated her for a week while I looked for a new home for her, but I did not get any interest. The separation time was not good, she was extremely stressed and anxious. I tried reintroducing her to the flock after the separation and her feather picking was even worse than before. She seemed to have a singular obsession with it. She had no interest in normal chicken behaviors like the rest of the flock, just simply seemed determined to stalk her flockmates and pull feathers out of their butts. Looking back and comparing her to my other chickens, it seemed to me like she had neurological issue. It was tough to make that call to end her life, but ultimately I think it was the correct decision for my flock because there has been peace ever since.
If I could do it over again, I personally would skip the week of separation for an anxious chicken with deviant behaviors like that. It only made her worse while stressing her and me out for a full week. If I ever had an issue like this again, I would just try to re-home her for a day or two and then cull her immediately if I had no takers.