Is it permissible for a Christian woman's 20-year-old son to be her guardian (wali) in the marriage contract, and is his consent to the marriage via a short text message (SMS) valid?

Marriage to a woman of the People of the Book is permissible, provided she is chaste. However, marriage to a Muslim woman is preferable. For the validity of marriage to a woman of the People of the Book, the same conditions as for a Muslim woman apply, including the guardian (wali) and two witnesses. Her infidel guardian (wali) oversees her marriage contract. If the infidel guardian objects to her marriage to a Muslim, the guardianship transfers from him. As for the order of guardians, it is permissible for an adult son to oversee his mother's marriage contract even if her father is present, according to the opinion of Imam Malik. Regarding the guardian's presence, it is a condition for the validity of the contract. His consent via phone is not sufficient; he must be physically present at the marriage ceremony. If the contract was concluded via phone, it is advisable to redo it, with the guardian deputizing someone to conduct the contract on his behalf.