If it is typical for this hen, and she has not taken to heart any top pecking order instructions from you, then I agree, she must go. I have had superior manners from my Hamburg hens and roosters for 40 years. I trusted them with my children, my grandchildren, and now my great grantchildren. Many other breeds can be more or even extremely agressive.
If you cannot keep new introductions to a flock separate by some wire for a while, (even if it is only one bird), give them plenty of places and space to outmaneuver an agressor so that they cannot get trapped in a small space and get beat up, or killed, by an extremely top pecking order hen. I have just introduced two young barred rock hens to my small flock of hamburgs and wyandottes and they are getting along fairly well, unless they try to pick up a treat an older hen sees first. They they get a hard peck. The rooster has been gentle with them from the beginning.
If you cannot keep new introductions to a flock separate by some wire for a while, (even if it is only one bird), give them plenty of places and space to outmaneuver an agressor so that they cannot get trapped in a small space and get beat up, or killed, by an extremely top pecking order hen. I have just introduced two young barred rock hens to my small flock of hamburgs and wyandottes and they are getting along fairly well, unless they try to pick up a treat an older hen sees first. They they get a hard peck. The rooster has been gentle with them from the beginning.