I disagree op, I think some women are doomed from the start to become nightmare mils.
My mil didn't stand a chance, she has all the hallmarks: Naturally passive aggressive, selfish, sulky, crass, rude, know it all, manipulative, entitled, over bearing. Its just a shame she had sons, I firmly believe that any daughter she might have had would have left her long ago and never looked back.
I would never treat my son with the level of disrespect and entitlement she treats hers with.
She had a vision of how his life would turn out that included her very heavily: What hos wedding would be like, his job, his house, and they all involved her being the 'manager' she never factored another woman into it at all. So she got a sharp shock when she realised we wanted to do things on our own.
Dh and bil were unknowingly responsible for her happiness and sense of self esteem, its utterly despicable to use your children as pawns in your own game of life.