Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him)
Is it obligatory for someone to attend a wedding feast if she knows that there are things there that are displeasing to Allah?
It is not obligatory for anyone 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 their 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 Allah, 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 Allah, then it is better that they do not attend.