see but don't touch for a while. Then pick a middle of the road bird, not the bottom bird of the pecking order, and put her in with the new bird for a while. There might be a flurry, but unless there is blood let them work it out. Leave them together for a good week. Then introduce the pair to the flock. If one of your flock is a real bully and very aggressive, put her in the pen the other two were in for a week until the flock is settled down, then add her back in.
A single hen addition is about the worse one to do.