What is the scope of a wife's responsibility toward her husband's mother in Islamic Sharia, and how can obedience to the mother and preservation of the wife's dignity be reconciled in cases of disagreements and insults from the mother?

It is not permissible for the mother to insult her son's wife. The wife's obedience to her husband's mother is desirable, not obligatory. The husband should strive to please his mother and persuade his wife to obey her. He should consistently maintain ties with his mother and family, and respond to ill-treatment with kindness. Whoever does so will have Allah as their supporter and helper.