Small flock of chickens hate ONE new chicken

Hi there,

I had a neighbor ask me to adopt their solo chicken after it's partner died, which I was happy to do, but it's been extremely rough trying to integrate her with my current small flock because they hate her. Every time they are together in the yard they pin her down and peck at the back of her neck. Here is the timeline of everything I tried:

• One month garage quarantine
• Two months of "through the fence" visual introduction with no physical encounters. During this time she frequently puffed up at one of my other chickens.
• Six Months living in a separate enclosure that is visible from the other (her own food, water, roost, next etc).
• Free range in the yard every weekend, where the flock beats on her relentlessly if they see her and she has to constantly run away. I'm hoping that these contact days would improve but they are not (maybe very slightly)

I'm not sure what else to try. I'd like everyone in the same run and coop during the day and to stop fighting. I have about 100 sqft per chicken in my run and a coop large enough for everyone.