We recently had a hen injured by a hawk (minor injury to eye, but closed and bleeding). The other hens were trying to peck her injury thinking it was something to clean off of her, but of course that hurt! She was scared of the others for awhile, and we had her sleep separately for a couple nights, but integrated her with the flock during the day. Then the same hen was attacked again! Both times my daughter was the one to see the hawk on her and scare it off. Her old injury was reopened and we had to sort of start over. We did short times outside by herself (with my daughter) and short times with the flock, and increased the time as long as all were working it out, pulling her in if the others got too aggressive or she got too freaked out. After a few days we tried her in the coop overnight and she was on the bottom rung. We had a cold spell and she was back up with the bottom row of chickens after a couple of nights! We have sweet chickens, but they were establishing a new order based on the injured chicken's weakness. As she healed/got used to her new vision in the injured eye, she seemed more able to rejoin the flock.
I wouldn't give up, but it may take some observation and protection if you want to help her reintegrate. The chickens are following their instincts for survival by having the strongest lead. She may need to get stronger or readjust something (her attitude toward the top chickens?!) to be able to fit back in.
Good luck!