Does she have pups right now? She may be just trying to protect them. Dogs are pack animals and will work on who is the leader (Alpha). If you have two Alphas - they will fight and not much you can do. I have two males (father and son). They always got along great and then one day they both tried to go out the door at the same time and the son step on his father's foot trying to get out. That did it. I even neutered the son, thinking this would stop it. Nope! To this day they cannot be in the same room. They are both lovable and very well behaved. They just don't like one another. Go figure!
T.