With some breeds it can be difficult to keep more than one female. I only have 1 female boxer as it's a breed that often can have same sex, same breed aggression. Since I only keep female dogs I am careful of what breeds I add to my pack. Females in general can be more predisposed to fight for dominance and resources. We humans sometimes create it by favoring one dog over the other, and giving it power.
I've never owned a pit bull so I'm unfamiliar with whether they are prone to female aggression.