Bamidbar 30:10

כל אשר אסרה על נפשה יקום עליה [BUT THE VOW OF A WIDOW AND OF ONE WHO IS DIVORCED] EVERYTHING WHEREWITH SHE HATH BOUND HER SOUL SHALL STAND AGAINST HER — because she is not under the control of a father or under the control of a husband. Scripture is speaking of one who is a widow after having been fully married (נשואה) (Sifrei Bamidbar 154:1), but in the case of one who becomes a widow after having only been betrothed, if her husband dies his entire authority becomes emptied (void) and returns to her father (Nedarim 70a).

וְנֵ֥דֶר אַלְמָנָ֖ה וּגְרוּשָׁ֑ה כֹּ֛ל אֲשֶׁר־אָסְרָ֥ה עַל־נַפְשָׁ֖הּ יָק֥וּם עָלֶֽיהָ׃

But every vow of a widow, and of her that is divorced, with which they have bound their souls, shall stand against her.