Feather pecking damage

Bernadette's feathers are just not growing back as I would expect. I saw a drop of blood on her back yesterday so sprayed her with the purple whatsit, but think Alice must still be nibbling on her feathers.

Originally thought it would clear up once Dorcus was gone as she was the main feather pecker.

Any ideas on how to help Bernadette? The spray for feather pecking doesn't seem to have any effect.

Bernadette is the one sitting down, hopefully you can see her back. Alice is the big black one looking over. They are actually best of buddies, and don't seem to ever have a cross word with each other so I'm flummoxed about the feather pecking.
Thanks Christine