What is the ruling regarding a sister's estrangement from her brother's wife's sister ("salafah") for approximately four months, knowing that there have been attempts at reconciliation from the estranged sister's side, and that she has been subjected to harassment from the other party?

Since abandonment and estrangement are forbidden in Islamic law, you must resume communication with this woman. What is required among believers is harmony, affection, and mercy, for they are like one structure and one body. If association causes problems, then let there be only salutations between you, and speech only when necessary, for that lifts the estrangement.