What is the ruling on shunning a mother-in-law if she was the one who initiated it, and is it permissible to perform Hajj while this situation persists?

The wife must honor and respect her husband's mother, and likewise the husband must honor his wife's mother. This increases affection and love between them. The Prophet, peace and blessings be upon him, forbade a Muslim from abandoning his brother for more than three days, and he informed that the gates of Paradise are opened on Mondays and Thursdays, and every servant who does not associate anything with Allah is forgiven, except for one who has animosity between him and his brother. So, hasten to reconcile with your mother-in-law and be the first to offer greetings, for whoever pardons and reconciles, his reward is with Allah, especially since you are about to perform Hajj, and this is an opportunity for reconciliation and freeing oneself from sins.