It is incumbent upon that woman to hasten to embrace Islam and not wait for separation from her husband or the like. There is no doubt that remaining in marriage with her non-Muslim husband is really less harmful than dying as a non-Muslim, may Allaah guard us against that.
However, she should invite her husband to Islam. If he embraces Islam before her waiting period ends, then their marriage is still valid as it is. But if he does not embrace Islam until her waiting period ends, then the marriage is cancelled and it is not permissible for her to allow him to have intercourse with her