What is the legal ruling concerning the inquirer's action of marrying a Christian woman in an 'urfi marriage, where she declared her conversion to Islam, and what observations can be made regarding what was mentioned, and what must be done?

The aforementioned marriage is invalid due to the absence of offer and acceptance, and the absence of the guardian (wali) or his agent, or witnesses. Consequently, the woman is still a stranger to you. It seems that the shaykh who issued the fatwa did not understand from you the absence of these conditions. To rectify the situation, the marriage must be completed according to Islamic regulations. A Christian woman's marriage is handled by her guardian from her own religion. If she converts to Islam and has no Muslim guardian, the Muslim judge or whoever acts in his stead will arrange her marriage.