It sounds like you have a bigger problem than reintroducing this chicken. It sounds like you have a flock harmony problem. Often this is brought on by issues in housing/care, like not enough space, feeders, water sources, hiding spots, things to do, etc. Sometimes it's brought on because a chicken is an odd one out, a bully, etc. and making life miserable for all. It would take some more knowledge about your setup and observation of your flock to make a good diagnosis there.