Mother-in-law - what is your role?

I wonder what the role of the mother-in-law is.

If she is a dictator in her own home, is she to teach a daughter who doesn't have the same nature to become the same as her?

Is she to work to oust her daughters' husband if he is not molten compliant?

Is she to promote a focus on any and every negative that is possible to perceive and misperceive in her son-in-law?

Is she to plant seeds that lead to her daughter beginning to hate the father of their joint child?

Is she to re-link the umbilical cord between herself and her daughter, so that the inherent laziness in her daughter is played to and an utter dependence develops?

If she is unable to completely dominate the son-in-law, so that both he and her husband are her lapdogs, is she to speak of mothers who have divorced and re-married as though it is a perfectly natural path to take? (..knowing this will give her much more time with grand-daughter..)