I recently added one pullet to my existing flock of 4 hens. The pullet was about full-size when I added her. It was definitely very hard to watch all the chasing and pecking, but it ended up turning out ok after a few weeks. What I did was provide hiding places for my pullet. One thing that I did was provide a tarp that blocked the view of one corner so the pullet could hide behind it. One end of the tarp was laid across the ground in the run, too, so when the hens got too vicious, the pullet would go underneath the tarp to hide. I also ended up having one bully hen that was a lot worse than the others, so I separated the bully from the flock for a week. When I put her back, she had a much better attitude. If you have multiple bullies, you can separate one of them from the flock at a time and adjust their attitudes sequentially.