Who is Mimi (Mum) Davis from The Moon Is a Harsh Mistress and what is their importance?

The "senior wife" and tight-fisted but tolerant de facto matriarch of the Davis Family, of which the protagonist and narrator, Manuel ("Mannie") Garcia O'Kelly-Davis, is fifth of nine husbands in a "line marriage" that includes four wives and 17 children, Mum is exiled to the moon for "carving a man under circumstances that leave grave doubts as to girlish innocence." She afterwards repents of "violence and loose living." Mum is Mannie Davis' favorite wife and first recruit to his covert revolutionary cell, with code name "Cassie." She quickly takes to fellow revolutionaries Wyoming ("Wyoh") Knott-Davis and Stuart Rene ("Stu") LaJoie, both of whom require sanctuary and later "opt" into the family, and the charming Professor Bernardo de la Paz. Mum professes no religion but never misses a Tuesday night service, when second-husband Greg preaches. Mannie recruits Mum because she is an able executive, respected throughout L-City, and in Luna for longer than 90% of the population. Without her, it would be difficult to use the phone. Mum has been silently longing for a revolution. Over the years, Mum opts out of family management and is succeeded by Anna