I could bore you with details but I'll be brief.
I lived with heII from due to Sayblee's aggression toward other dogs until she died. She was my heart dog, utterly loved and loving to me. But she tried for 5 yrs to eat the 70 pound chow, once even took on the 90 pound Rottweiler (only once, thank goodness, because running 3 packs would have been beyond belief). She got her championship last major with stitches in her head (judge said, I kid you not, "Nice stitches!")
I could have them in my bedroom together as long as I was there but I actually had to pin the bed covers to end of bed to make SURE if she got up at night I knew and was alert to avoid issues.
The chow was velcro, could not have made her sleep elsewhere. (she was a rescue, actually chow/coyote mix and once she actually had Sayblee by the stomach as I jerked her up. I knew she was going to gut her right there in my arms, but when I yelled NO she spit her out without even a mark.) The only reason Sayblee survived is both the Chow and Rottie had no desire to hurt her, just merely to get her off them. I couldn't bear to place Sayblee and placing Katana, the chow/coyote, was really not an option. So I coped.
Then, at 6 she had a fight with Arwen and they could only go out under direct supervision after that.
When I spayed her I got a lot of flack from the breeder and a few other breeders. But my contract was to show her, not breed. She was utterly over the top dog aggressive, going window to window tracking the neighbor's loose mini dachshund. I told them if she EVER got loose, there was no way we would get her off before she killed him. Fortunately they gave the dog away before a car or Sayblee got him. Breed her and pass that on? Not responsible. I don't care how normal dog aggression is in the breed, she was insanely obsessed and should not have passed that on.
Arwen never wanted to be top dog. Cara has no desire shown to lead. Hopefully they will live happily together forever. But right now I won't even bring in a foster for fear of changing things. And I always tell people, you get a new dog, you do it knowing one day you may have to keep separated for life. It happens. Can't risk it? Keep the dog or pack you have now because it can change in a blink.