My female Dane attacked my female Mastiff?

We have 3 dogs, all unaltered, 3yo m Bull Mastiff, 2yo f English Mastiff, and 3yo f Great Dane. Had the Bull first at 9mo old, got the English 6mo later at 6mo old, They are great together, play, sleep, eat etc..Dane came into the pic 1 yr later @ 3yo. Got from newspaper, guy had no time, supposedly raised w/ another female. little shy @ first. but settled in fine, We had for 10 months now, all sleep, eat. play well together, mostly the 2 mastiffs play together, the F very much a puppy and always the submissive one, the Dane will join in a chase every now n then,but not really the wrestle play type like the other 2. although, Dane, never aggressively, would try to lay in her favorite spot, whether another dog was already laying there or not. does the nudge thing "pet me" to people, nudges her way to the front line when giving attention to the other 2, and occasionally tries to hump the male, all domination traits i'm told. Well, yesterday my roommate came home to find the 2 females bloodied up and panting hard, I think if he hadn't come home when he did, it would have been a lot worse. But my F Mastiff was chewed up pretty bad, her throat and mostly her ear. The Dane was fine, Vet said Mastiff may be coming into a heat, the females have to be separated indefinitely and that the aggression will only escalate. She did'nt say anything about spaying fixing the problem. Does anyone have any suggestions on what to do now?? I currently have the Dane and the Male separated from the injured mastiff, can I trust the Dane with my male, can I ever trust her again with the other female? Please help, will spaying fix this or is it too late at this point?