So you have three cockerels and a pullet. I would separate her ASAP, because if it’s not happening already, those males are going to harass her to no end. Cockerels reach sexual maturity earlier than pullets, so she won’t be willing to mate. That often leads to a cockerel being rough with the pullet, possibly injuring her. Especially if there is more than one cockerel. It’s also likely that they will gang-breed her - one knocking the other off so he can also mate her.