Is it permissible to inform a brother about his sister's husband's threat to expose her and demand a divorce, knowing that she has repented and mended her ways?

This woman has excelled in her repentance from the sinful relationship, and her sister's husband erred in spying and threatening to expose her. The woman is advised to supplicate to Allah, remind her sister's husband of the punishment for exposure, and if he proceeds to expose her, she may deny that she did so by using ambiguous statements (ma'arid). It is not permissible for her to seek a divorce from her husband without a legitimate شرعي reason.