What are the rights of the husband's sister over the wife, and is the wife sinful for shunning her due to her continuous harm?

Among the good marital practices is for the wife to treat her husband's family well, and to help her husband in honoring his parents and maintaining ties of kinship, and to overlook the slip-ups of his family. What the questioner mentioned regarding her good treatment of her husband's family and her financial assistance to her husband for their expenses is an act of benevolence and noble character. The behavior of her husband's sister is far from the ethics of Islam and contrary to sound human nature, for reciprocating good with good is among the ethics of Islam, while insults and slander are forbidden. Therefore, she should advise her husband's sister and remind her of the ethics of believing women, and supplicate for her guidance. She is permitted to shun her for only three days, and after that, she may limit interaction to the extent that avoids estrangement, unless there is a legitimate benefit in shunning for more than three days that would improve the situation. And she must help her husband maintain ties with her.