Is it permissible for a Christian girl to marry a Muslim man secretly, and without the knowledge of her guardian, because she fears her family?

It is permissible for a Muslim man to marry a chaste woman from the People of the Book. The conditions for the validity of this marriage are the consent of the woman and her guardian, the testimony of two Muslim witnesses, and the dowry. Her guardian is someone who shares her religion. A disbeliever has no guardianship over a Muslim woman. If she embraces Islam, her guardianship transfers to her Muslim relative, or the Muslim judge marries her off if no such relative exists.