What do I do?

[Flip Flop]

I have two Holland and two Orpington hens and they all bully one chicken that looks like a mix between the two. they peck at her and force her into the coop. She has a section that is missing feathers but I don't know if that was the other hens.

 

[Lor]

Can you tell if there is a worse offender? Maybe one who starts it?
If so, maybe that one could go into a pen removed from the flock for a day or two.
The only other thing to do is put the picked on one in a pen by herself for awhile. Inside where she is still a part of flock. "(See but no touch" method)

 

[Flip Flop]

I just found out that all the jens peck at each other but most of the time when I see them they peck the odd one out

 

[Lor]

Maybe she is at the bottom of the pecking order.

 

[aart]

How old are these birds, in weeks or months?
Have they always lived together or have you added new one(s)?
How big is your coop and run, in feet by feet?
Dimensions and pics would help immensely here.