Does the wife sin for supplicating against her husband's brother who wronged her and slandered her, and what is the most appropriate approach for the husband to deal with his brother in this situation?

If the man has wronged the questioner and responded to her kindness with malice, then it is incumbent upon her husband to advise him, enjoin him to do good, forbid him from evil, and not allow him into the house in a way that causes discomfort. It is not permissible to completely sever ties of kinship with him, for severing ties of kinship is among the major sins, unless it becomes the sole means for his reform or to avert his harm. The husband's brother is not a *mahram (definition)*, and the questioner is not obligated to maintain ties with him. It is permissible to supplicate against the oppressor to the extent of his injustice, and it is not permissible to do so beyond that. However, it is better to refrain from it because it is a form of self-vindication, as Imam Ahmad said: "Supplication is retribution." And forgiving the wrongdoer increases the forgiver in honor, as the Prophet, peace and blessings be upon him, said: "Allah does not increase a servant who pardons except in honor." And it is a path to attaining Allah's pardon and forgiveness. Allah the Almighty says: {And let them pardon and overlook. Do you not wish that Allah should forgive you?}