IME, all of my female dogs got along well with both sexes, until they were 2. Then, I had to keep 2 females separate, forever. It's funny, my males were the same way, all changed when they were 2
I only kept 2 females if I realized they may have to be separated - was I willing to do the extra work if I did?
No matter how I tried to get 2 dogs to live peacefully together, if 2 dogs hated each other, they hated each other and I could not trust them to be together.
It really helped to neuter a dog, but that certainly was not a for sure thing.
The way I looked at it, I didn't ask the resident dog their opinion on getting the other, so I couldn't see them living together peacefully if they were thrown into the situation.
I had better luck with my kids. The rule was "You don't have to like each other, BUT you have to act like you do." It doesn't work with dogs.