tonight or tomorow night you should put the new hen on one of the roosts aparently when they wake up they dont fight as much but you will just need to let it play its course she seems to want to be leader.
but if after a month they are still fighting you may need to get ride of her
good luck...
because you already had your birds they had a peacking order but when you add a new one you have tacken the peacking order apart you justy need to leave them together and soon the new one will have her place and there will be no more fighting