Answered by Sayyidi al-Ḥabīb `Umar bin Hafīẓ (may Allāh preserve him and benefit us by him).
Is it obligatory for a woman to attend a wedding feast if she knows that there are things there that are displeasing to Allāh?
It is not obligatory for a man or a woman to attend a wedding feast if they know that transgressions of the Sacred Law will take place there. The individual must then weigh up what will be the consequences of his or her presence or absence. If a person can attend without participating in an act of disobedience and without condoning it and at the same time can be of benefit in calling people to Allāh, then it is better that they attend. If, however, that person by attending will participate in act of disobedience and will not be able to call people to Allāh, then it is better that they do not attend.