First: The marriage that took place between her and her Christian husband is considered valid in Islamic law. Marriages of non-Muslims are recognized as valid among them if they fulfill the essential requirements according to their religion and customs, and are not inherently prohibited (such as marriage to close blood relatives).

Second: If the divorce took place in accordance with their recognized legal system and was issued by the competent court, then it is considered a valid divorce in Islamic law. The Shari‘ah acknowledges the personal laws and rulings of non-Muslims regarding their marriages and divorces when these occur while they are non-Muslim.

Accordingly, if the divorce was officially finalized and the marital relationship legally terminated, and her waiting period (‘iddah) has concluded, which is three menstrual cycles if she menstruates, three months if she does not menstruate, or until delivery if she is pregnant, then she does not require another divorce.
After embracing Islam and completing her ‘iddah, she may marry a Muslim man with a valid Islamic marriage contract fulfilling all required conditions and pillars.

However, if what occurred was merely separation without a legally recognized divorce according to their system, then the exact circumstances must be verified before proceeding with a new marriage contract.

The majority of scholars hold that the marriages and divorces of non-Muslims are recognized as valid among them when conducted according to their laws, and there is no requirement to repeat the divorce after accepting Islam.

Therefore, the basic ruling is that her divorce is valid if it was officially documented and recognized in their legal system. She does not need a new divorce, but it must be ensured that her ‘iddah has ended before entering into a new marriage.