Muslim women are not allowed to marry men outside of Islam.

I am sure it does happen, and can work. But there needs to be a respect for both religions. My wifes cousin, a catholic, married a muslim. It seems to be working fine. They seem to be happy.

A bit unorthodox, but it can work. The shallow end of the Islam pool coincides with Christian morality, though even if she is the perfect wife for him, she could bring big baggage, meaning male relatives that do not like this marriage and/or her husband.