Is quarreling with an unjust sister a sin, and does it affect the acceptance of good deeds, if the quarreling is due to her injustice and incitement of the family, and the fear of renewed problems with her?

Abandoning speech with one's sister is considered a forbidden boycott (hajr muharram), and the one who does so is sinful if it exceeds three days, because it is an abandonment and severance of kinship ties (qati'at rahim). The Sacred Law has severely warned against it, and it is an impediment to Allah's forgiveness and the acceptance of deeds until the disputants reconcile. Harm from a relative does not permit cutting ties; rather, it is obligatory to maintain kinship ties, even with the lowest degrees of connection, and to be patient in the face of harm.