Bully Aseel Hen?

Hi

I have 4 hens and one rooster in my flock, few months ago my brother bought a Aseel hen in to our flock and the Aseel hen was getting along with the flock just like any other hens would.

but after a few weeks the Aseel hen started bullying one of my little hens, it is always pinching the hen and chasing her around the garden, soon as she comes out of the coop it pinches and chases her, it wont let her come near any of the other hens or near the food.

now the little hen stays inside the coop and if she comes out she goes under some pallets and stays there, so in order for me to get her out and let her roam around the garden and eat with the rest of the flock i have to put the aseel in the run so she is locked inside the run, only then my little hen will come out and roam around and eat with the rest.

how do i fix this problem without having to lock the aseel inside a run? please someone help?

Thanks.