X2. Adding a single new bird to a flock can be very difficult. I've done it in the past, I will not do it again! Once the bird is the same size as the rest, fence of part off the run for her and give her a dog crate or similar to sleep in the coop at night. That way they can get used to seeing her but not attack her. It would be a lot easier if there were at least two or three, one is going to be hard. If you have any possible way to get a couple more her age I'd highly recommend doing so, then you can integrate them as a group. Regardless, go slow with it, take your time. I had one instance where I was trying to integrate a single new bird and they never did accept her in the coop. She was allowed to free range in the pasture with them but they would attack if she tried to roost in the coop. I tried for months to integrate, never worked. So just be prepared to take time doing it and for the possibility that it may not work. Best of luck.