Can I assist in a wedding where the sexes mix if I wear Hijab?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

It is Haram to participate in a wedding party, if there will be something Haram such as mixing between males and females and music as long as one cannot change what is wrong and prohibited; because participation in such things constitutes a form of acknowledgement of wrong and helping its followers. No doubt, most wedding parties today include Haram.
Ibn Qudamah , while commenting on invitations to parties in his book al-Mughni, said: 'If one is invited to some banquet that includes some disobedience such as serving wine and playing music instruments, he has to attend if he can change what is Haram and evil, since answering your Muslim brother's invitation will help you to fulfill two obligations: satisfying the invitation and changing evil. But, if one cannot change what is wrong and Haram, he should not be present' .
As a result, we state you are not permitted to attend such parties if you cannot change what is wrong and Haram even you wear your Hijab.
Allah knows best.