I have a wife who gave birth to eight children. One of my daughters is used to go out without my permission. Once I beat her and her mother reproached her and cursed her and her father and forefathers.
Six months later, the girl went out without taking my permission. I beat her again and her mother cursed my mother three times. I was greatly offended by this insult. It is worth mentioning that I helped my wife to memorize two Juz' (a 30th of the Qur'an) as well as the text of Al-Usul Al-Thalathah (The Three Fundamentals). Nevertheless, this has not deterred her from cursing me and my parents. Please give me your Fatwa (legal opinion issued by a qualified Muslim scholar).
If the reality is as you mentioned, the curses the woman uttered signify disobedience to Allah (Glorified and Exalted be He) and an offence against the daughter, her father, as well as her grandmother. The wife has to make Tawbah (repentance to Allah) by regretting the sin, giving it up, and being determined not to commit it again. She should ask for the forgiveness of those whom she cursed. Allah (Exalted be He) says:
O you who believe! Turn to Allâh with sincere repentance!
(Part No. 19; Page No. 239) He (Exalted be He) also says:
Say: "O ‘Ibâdî (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allâh: verily, Allâh forgives all sins. Truly He is Oft-Forgiving, Most Merciful.
Scholars agreed that this Ayah (Qur'anic verse) was revealed with regard to the penitents. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.