Even though she swore that she would not attend the wedding, she should not persist in that oath by absenting herself. Instead, she must offer the expiation for her oath (kaffārat al-yamīn) and go to the wedding, for her presence brings benefit, maintains family ties, and removes potential harm. Accordingly, she should break the oath, attend, and make the expiation, for Allah says: “Allah has already prescribed for you a means to dissolve your oaths” (al-Tahrim 66:2).

Consecutive fasting in the expiation for an oath
Question: I owed a number of fasting days as expiation for an oath, so I asked one of my sisters—whom I trust because she has some knowledge—whether the fast had to be consecutive or could be separated. She told me that consecutiveness is not required, so I fasted the days separately. Later I heard on the radio program “Nūr ʿalā al-Darb” from one of the respected scholars that consecutiveness is required. I returned to her, and she produced Ibn Kathīr’s Exegesis, which cites Mālik’s opinion that consecutiveness is not required. Am I at fault, and what is the correct view on the matter?
Answer: As you noted, scholars differ on whether the fast of expiation for an oath must be consecutive. The stronger view is that of Imām Aḥmad, Abū Ḥanīfah, and al-Shāfiʿī in one of his two opinions: the fast must be consecutive, because there is a Qur’ānic reading that states, “then fasting three consecutive days.” This reading is an explicit text making consecutiveness obligatory. Allah knows best.