What is the Shar'i ruling on the stance of a mother who supports her daughter in severing ties with her sister, and is aiding in severing ties considered one of the major sins? Is it obligatory for the mother to shun her daughter so that she may return to upholding kinship ties, and what is the advice that should be followed in this situation?

A mother is obligated to strive for reconciliation between her children, and it is forbidden for her to cause a rupture between them because it is a grave sin. Estrangement is not permissible except for an overriding benefit. Do not accuse your mother of potential actions; rather, find excuses for her and try to understand the true reason for her stance.