I have observed that a woman always takes the side of other women against a man unless she has a particular attraction or allegiance to that man. Women are very competitive and will fight another woman over a man if he is Her Man (or a potential Her Man), but will not engage in a fight with another woman on behalf of a man that she has no feelings for (not Her Man and no desire to make him Her Man).
In simple terms a woman is on two teams: Team Woman and Team Her Man.
Team Her Man is her primary allegiance and she will go against Team Woman if she has a Team Her Man.
But Team Her Man is a more fluid and ill-defined concept. It can be an unbelievably strong loyalty but can quickly slide into nothing if she loses respect for Her Man. Most women have no Team Her Man but desperately want to be on such a team.
Also other women will actively fight against a woman that puts Team Her Man first. Happiness is found on Team Her Man and so any woman that does not have a Team Her Man tries to recruit a woman back to Team Woman so that all the women team members can be miserable together.
The irony is that any woman that tries to sow discord in another Team Her Man does great damage to all other Team Her Mans and thus hurts herself too. There is just too much comfort in the shared misery on Team Woman and they can gripe about the happy women that are on a winning Team Her Man and against the imaginary Team Man. The members of this Team Woman don’t understand the concept of the greater good.
There is no Team Man, because men don’t give a shit about other men. The women on Team Woman think they are fighting against Team Man (aka Evil Patriarchy), but Team Man never showed up for the fight.
So in our modern world, Team Woman is predominant and is changing the rules to make it easier to win against an opponent that never showed up for the fight.