Libertree - I would not expect a red sex link chicken who was not broody to accept chicks. Often times the lowest bird in the pecking order is the meanest to chicks or new birds.
Adding a single bird back to a group, seldom works. What might work, is to take a middle bird from the flock, and add her to the victim. They will probably have a dust up, but it is one on one, and it should soon settle. Leave them together for a week.
This is a lot of fiddling around, but it can help. Then take the original flock, if you don't have too many and put them in the small pen, and let the victim and new partner into the old set up for the day. Then let everyone go to the coop that night, but do it just before dark. 
Or you can add the pair back to the flock, and watch, pulling the first and second bird, and maybe the third bird that attacks, and put them where you had the pair. If the 4th bird and so on attacks, leave them with pair, maybe breaking it up with a squirt gun. But try and let them work it out as much as possible.
A week later, add the original meanies back into the flock and watch carefully. You may want to get some pin less peepers. Many people with this issue with a small flock swear by these.
Do have multiple feeders placed so a bird eating in one spot cannot see birds eating in another, hideouts, and get aways set up in the run. Pallets, up on blocks, leaned against a wall, saw horses, ladders - places birds can get out of sight from each other can really help. I call it clutter, it will look more cluttered to you, but actually uses a lot more of the vertical space and more interesting to birds.
A lot of fiddling around, but usually works.
Mrs K