What is the ruling on maintaining kinship ties in a case where a sister is expelled, threatened with sodium, and asked to divorce her righteous husband?

The sister should endure the harm from her sister to earn rewards. It is not obligatory for her to visit; rather, communication can be maintained by phone or writing, and gifts can be sent. It is not permissible for her to seek divorce from her righteous husband, due to the Prophet's (peace be upon him) saying: "Any woman who asks her husband for divorce without a sound reason, the fragrance of Paradise will be forbidden to her."