You just need to separate her so she isn't the boss any more. when you put her back she'll have to find a place in the flock again and hopefully not at the mean top hen.
She is being intimidated and bullied. Your lead hen can make her life miserable and even starve her to death. Take the lead hen out of the flock. Pen her up away from the flock and see if the other bird improves. You will shake up the pecking order. In about a week or so bring the bully hen...
It takes time to get used to a new home. Make sure feed and water is where she can get to it easily without having to venture too far from her safe place.