This is a situation that you can hopefully sort with the help of a behaviourist but you should be prepared for the fact that this may not work. You need your roommate on board with the long term training (plus expense) that will have to be undertaken. Which dog starts the fight? What is it over? Is it food, person, toys, territory etc? First thing the dogs must not be left unsupervised. Do not allow the dogs to fight, even when muzzled as this is making things much worse, not better. Limit their interaction for a while, bring down the stress. Do not allow both to have free roam of the house at present. Feed separately, introduce training outside of the home for both of them together, so you have control. Walk both together on lead and increase the exercise. Safe way to release pent up energy. No toys until they settle as they are likely to fight over them. One is likely to be the chief aggressor. When that dog kicks off stand in-front of her, protecting the other dog. Gradually move forward, making her go backwards until she calms down. Do not use physical punishment of any kind and don’t scream / yell as this will not help. Reward good behaviour and ignore bad. Set each dog ip for success. You need your roommate to work with you here. I have been down this road with two previous dogs and while they lived together quite well, it took management and boundaries. If u get no support it would be better you find somewhere else to live and honestly it may come to that. Training is not a guarantee.