What is the ruling of Islamic law regarding shunning a sister who curses and assaults her sister, her sister's husband, and her mother, incites discord, does not respond to advice, and persists in her harmful actions, while the family believes that distancing themselves from her is the solution?

It is not permissible to abandon a sister merely due to a disagreement, nor to refrain from visiting one's parents because of it, for the Sharia has forbidden estrangement and abandonment among Muslims, and cutting off ties of kinship is among the major sins. It is obligatory to maintain kinship ties even with those who sever them. What a person feels in their heart towards their sibling is from the whisperings of Satan, who seeks to corrupt relationships, therefore one must seek refuge in Allah from him, treat her with kindness, and supplicate for her well-being. Responding to evil with good brings affection and repels the stratagems of Satan, and forgiving those who do wrong increases one's honor and dignity, and it is a path to attaining Allah's forgiveness.