I have two easter egger hens and two black sex link hens. The BSL have always been dominant, but lately it's getting worse. One of the BSL was pecking at the easter egger and started sititing on her. Any info would be helpful.
Maybe it's time to put the worst offender in chicken jail for a few days. Crate her out of sight of the others. It's possible when you reintroduce her she will find herself knocked down a peg or 2. If the abuse continues you may want to consider removing her from the flock permanently.
I had a similar issue with my BSL hen - her flockmate, also a BSL was very shy and retiring. My RIR hens would squabble with the BSL who was the head hen. Once they got past the teenage hormones stage, everything settled into place. I think yours will too. Just make sure the hens being bullied have a place to go where they can escape the notice of the BSL until things settle down. You can't stop them from being chickens and that's part of their developmental cycle. The other poster had a great idea too, if you want to try that. Generally, when they are out of sight, they are out of mind. When you reintroduce her, she may no longer be head hen and will act a little nicer .