Is the secret marriage of a divorced woman, by giving power of attorney to her immigrant son (who is in another country) to an unknown person, invalid, especially with the husband demanding conjugal rights?

A woman's marriage is not valid except with a guardian, who is her father if he exists. If he does not exist, then it is her son. A woman cannot appoint her son as her agent for her marriage, as she does not have the authority to عقد it for herself. Nor is it permissible for the guardian to appoint someone else as long as he is present. For the marriage to be valid, the Thayyib (previously married woman) must give her explicit consent, not merely remain silent. Accordingly, the aforementioned marriage is invalid, and the husband does not have the right to demand that the woman be handed over to him. It is advised to persuade the husband to divorce, but if he does not accept, there is no blame in disregarding him, as an invalid marriage does not require a divorce.