How can one marry a Christian woman who has converted to Islam while she is still legally married, given that there is no divorce among Christians?

If a woman embraces Islam while her husband is not Muslim, her marriage to him is annulled, unless her husband converts to Islam before her 'iddah (waiting period) ends, in which case the marriage remains valid. If he does not convert and her 'iddah ends, she is permitted to marry, and her marriage is legally valid even if, in official documents, she is still considered married to her disbelieving husband. To avoid the dangers resulting from not annulling the civil contract (such as the inheritance being established for her first husband and her children being registered to him), it is necessary to officially and legally annul the marriage.