Try to pay attention to what sets her off. You have to keep a very close eye on her and try to recognize her body language so when you see her going into her fight mode you can defer her. By this I mean, as soon as you see her stiffen up, ears go back, any type of growl, etc. you must immediately in a stern voice tell her NO! or I say Knock it off! If she does not immediately stop her behavior she must be separated either into another room or into her crate. She must learn she is not the boss, you are. I have this situation with my three bulldogs. Frankie and Jack are very passive and brutus is the alpha. This is ok because they all understand that I am the leader and must listen. Brutus still has his moments and I am always on high alert when they are all together. Brutus has actually learned when he is feeling out of sorts to go and sit in his crate and I will shut the door and give him the space he is asking for. Sometimes it is 10 minutes sometimes it could be a couple of hours that he wants to nap. Just last night all three were in the living room and Brutus jumped on the couch and just the idea of Jack in the same room was upsetting him. I could physically see his whole demeanor change. He became very rigid, his ears went back, he looked very nervous and let out a very low growl. I immediately put Jack in the kitchen and sent Brutus to his crate for a time out telling him he was not allowed to growl and act like that. I swear he understands me. He stayed in for approx. 20 mins and came out fine and ready to accept Jack in the mix. The key is to never allow the aggressive behavior to happen. It is a pain, but you really have to have eyes on them 24/7 if this type of behavior is happening. Good luck and keep us posted on your progress.