You ever tried letting them out differences on neutral turf like can be supplied with a larger pen? My bullstags are pretty clear hen they pose a threat to a pullet or hen so if interest is for a breeding where I do not have to watch all the time, then I put them in a pen neither knows with a couple extra roost poles and a nest the hen can get into where stag cannot get on top of her even to peck. Preference is to use 10 x 10 dog pens but 4 x 5 x 4 bird pens can work also.
Another option my be to place her in with a confident cock that will put her in her place but go no further, then while in that brief mind set where she does not feel like she owns the world. you can try to put her in with stag of your choice.