One hen bullying another very specific hen

Sex links are not nice birds in my experiences. They tend to be more aggressive than other breeds or mixes.

Birds have been molting strangely since last fall so some hens are still at it.

Occasionally a hen is so uncomfortable during her molt that she starts acting odd and skiddish which can cause some birds to go after them. It starts a vicious cycle where the picked on bird becomes chronically frightened and the more dominant members keep picking on it.

If your set up is big enough with plenty of hiding spots the picked on one can hide out and get away. Smaller set up can cause things to get worse. You didn't say anything about how large your coop and run is, so adding that could help determine if it's contributing to the problem.

You will need to either choose to stay out of it and hope it stops or you could separate birds to see if it helps. I would remove the bullies for a few weeks if you wanted to do so.

Sex link hens can become deficient in protein due to their high production. If you are feeding a layer ration it often isn't enough. It can cause aggression problems. I recommend a feed closer to 20% protein, especially if you feed anything else.