Is it permissible to marry a Christian woman who is still married and has not yet been divorced, or to annul her previous marriage in an Arab country?

The mere separation of a wife is not considered a divorce. It is not permissible to marry a married woman, based on the Almighty’s saying: "And [prohibited to you are] married women." It is permissible to marry her after her divorce and the expiry of her iddah (waiting period). If she is harmed, she has the right to seek divorce in the Sharia courts. You must immediately sever your relationship with her, as a relationship with a non-mahram woman is forbidden, especially if she is married. If you are the cause of her seeking divorce, then you are a mukhabib (one who corrupts a wife against her husband), and takhbib (corrupting a wife) is forbidden. Maliki jurists have even held that it is not permissible for a mukhabib to marry the woman he corrupted. A Muslim's marriage to a woman of the People of the Book is conditional upon her chastity, and it is preferable not to marry them in these times due to the numerous risks involved.