Is it obligatory for me to reconcile with my husband's mother despite her mistreatment of me and her refusal to reconcile, for my husband's sake?

A wife should be patient with her husband's mother and be dutiful to her. The husband is not obligated to obey his mother in divorcing his wife if the marriage contract has been concluded, unless there is a valid Sharia-compliant reason. The husband must strive to convince and appease his mother.