What worked for me in the end was totally isolating the bully out of sight of the others for a fortnight. I then cleaned the henhouse and zapped all the surfaces with neat vinegar to mask all smells. When I returned the bully that evening I sprayed all the hens with a 50:50 dilute solution of cider vinegar. Over the next few days I would spray Marie with the vinegar solution if she attacked anyone - she got the message and everything calmed down.