السلام علیکم ورحمة الله وبركاته
There's a new Muslim woman who's getting married. Her family have not accepted Islam. For her nikah she's sending a Muslim man to represent her as her wali for the عقد النكاح, is this the correct method and will the nikah be valid? Or does she have to go to the masjid herself?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
The nikāh would be valid with the Muslim man serving as the woman's wakīl (agent) to represent her and conduct the marriage on her behalf. She does not have to go to the masjid herself; sending the agent would be sufficient.
From an Islāmic standpoint, the appointment of the agent can be performed by any means (orally or in writing, in person, or over the phone, with or without witnesses). However, having seen several contemporary cases where women have claimed coercion into marriage, we recommend appointing the agent in writing and in the presence of witnesses, in order to protect against any future disputes.
At the masjid, in the presence of the groom and the witnesses (two male, or two female and one male), the agent will say: "I, being the agent of such and such woman, daughter of such and such person, have given her in the marriage to such and such man for 'x' amount of dowry. Then the groom will reply by saying; "I have accepted such and such woman in my marriage in the presence of the witnesses".
Only Allah knows best
Written by Shaykh Umer Khan
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 al-Fatāwā al-Hindiyyah, 1/324