I have seen this before. A friend of mine had a flock of chickens. She got a new batch which included an "exotic" variety. For some reason, this bird was very defensive, submissive, etc...As soon as she started running, the other birds realized they could intimidate her and they ganged up on her. We found her that afternoon all ripped apart. Guts everywhere. It was quite awful. When introducing new hens, I always put them in a seperate pen where the other chickens can see them. Keep them there for, oh...4-5 days. Then I would release them into the flock. Generally when I release them, the doors to the coup are open and all chickens are allowed to free range. I do this because I believe confinement is stressful to birds. I keep a close watch for about 20 minutes. Any bird being singled out and tortured is put back into quarantine for a few days and then reintroduced under close observation. Some birds take more time to adjust than others. The birds will fight a bit, but they are just figuring out pecking order. It's the fights that just don't stop that are a problem. If a bird is being attacked, she runs away and the aggressor chses after her and won't relent, then it's too soon. Good luck!