Pecked tail feathers

I have three Rhoad Island Reds who are 1 year old. Recently I introduced another hen who is the same breed who is two years old. I had to pull her out of the coop and bring her in the house to keep in a big dog pen because the others have picked at her so much there is a large bleeding hole in her back. I plan to keep her in the house for a few days because of cold weather coming in and to give her back some time to heal. I plan to separate off a section of the coop and keep her by her self for awhile except when free ranging. and slowly reintroduce her to the group. Are there any techniques anyone has used to successfully introduce a new bird to the flock?