In most of the in-law stories, it is the ggpps' fault. But it is a different story here.

The key of any relationship is mutual respect. This mm does not respect her mother-in-law at all. It seems that she is very spoiled -- staying at home all day without doing any housework, staying up late when knowing that her husband need to go to bed early, annoy her mother-in-law intentionally by making noise at night. If that is not selfish and mean, at least is not caring or considerate.

Her mother-in-law also has her own problems, but not oustragously bad.