
Spaying rarely makes any difference in hierarchy issues between bitches.
Personally I have found a good drubbing of both is needed.
It may seen that one starts it, but ti actually takes two.
what you perceive as the one growling at the other for no reason may actually be growling at the other for getting above itself and not giving way/respect.
So Ripley walks past Sadie or goes to lie near her and the other growls I would have them both sent out of the area, so neither gains from the behaviour.
By telling the growler off you may inadvertently be telling the one trying to raise her rank that she is entitled to do so.
I have had these issues with my pushy youngest and my currently nominally in charge eldest, first at puberty of the younger and recently when the youngsters pups were newborn.