What is the ruling regarding a girl's refusal to attend the weddings of her mahrams – including her brother – if they involve forbidden things like mixing of genders, immodest display, and singing, in order to help the women with washing dishes and serving the female guests?

It is not permissible to attend weddings that include reprehensible acts, except for those who denounce them; based on the words of Allah Almighty: "And those who do not bear witness to falsehood, and when they pass by [something] meaningless, they pass by with dignity." This applies equally to relatives and non-relatives. However, it is not obligatory to completely avoid the wedding; rather, what is obligatory is to avoid the place of the reprehensible act. It is permissible to participate in aspects that do not include forbidden matters, such as preparing food.