As far as I know (this is not a Fatwa) Muslim Women or Men are allowed to marry followers of Monotheistic religion, such as Christian and Jews. However, most Muslim Scholars do not admit that. Anyways, Legally it is allowed for Muslim girls to marry non Muslims in many Islamic countries (may be few exceptions) but from the religious point of view it is probably not.
One common statement made in general that Muslim boys can marry non-Muslim girls but the Muslim Girls can not marry Non-Muslim boys has no religious base. It is just something made up by greedy and immoral Men (Probably Muslim men).
Anyways, there is a probability that if a Muslim woman marries a non-Muslim man, the man may convert to Muslim. In that case no need for the question anyway. Hope this answer is reasonable enough.
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