Will the deeds of two sisters be raised (to Allah) due to their constant quarrel, even though one of them loves the other and does not allow her to be spoken of ill, while the other might participate in slandering her?

The Sharia prohibits shunning and turning away from Muslims. The sin becomes graver if the shunning prolongs, and it intensifies if it is between relatives, such as sisters, because it constitutes cutting off ties of kinship, which we are commanded to maintain even with those who sever them. Moreover, shunning is a cause for delaying the acceptance of deeds and the forgiveness of sins.

It is not permissible to shun a sister. Any rancor in one's heart is from the whispers of Satan, who strives to corrupt relationships. To rid oneself of this, one should seek refuge in Allah, think well of her, treat her with kindness, and counter Satan's whispers by supplicating for her well-being. Furthermore, responding to evil with good fosters affection and protects against the evil of Satan. Initiating kind words, even if it feels forced, removes grudges and brings about love.