why does my female figther fish keep attacking my male fighter?

[Jessica A]

She keeps biting his tail and dragging him to the bottom of the tank and then she just wont leave him alone he is so scared of her that he has hid in the red plastic plant we have in the fish tank for them im getting worried and im thinking my female fighter is a male when my cousin gave her to me he told me she was a female and im scare she is going to bite him hard one day and he we'll attack her as if she is a male fighter.