Is marriage to a Christian woman who converted to Islam and then apostatized valid, and what should the husband do concerning the usurious loan he took before his repentance?

If a woman marries after embracing Islam and completing her 'iddah (waiting period) with a lawful marriage, then your marriage is valid. You must strive to reform her and guide her back to rectitude, seeking help from righteous people. If she repents, maintains her prayers, abandons alcohol, and obeys you in what is good, then keep her. Otherwise, divorce her, because divorce becomes recommended or obligatory when a woman neglects her obligatory duties towards Allah, such as prayer and the like. It is not permissible for a man to remain with a woman who does not pray.