Is a wife's failure to communicate with her husband's stepmother considered a sin, especially if the latter mistreated her?

If your father's wife has mistreated you without justification, she has committed a wrongdoing. However, the guidance of the Prophet, peace and blessings be upon him, is forgiveness, overlooking, and not seeking revenge for oneself. Therefore, we advise you to forgive her, contact her, and inquire about her well-being, as this constitutes righteousness towards your father and kindness to him. As for abandoning contact with her as a form of boycotting, there are specific regulations that must be observed.