In most of what I've read, as well as my college master's theology prof, says the Hebrew term is one we don't have a perfect translation for.
"It" would be the closest thing, although it is not personable. The word there is
ambiguous . And here for the sake of other views is
an article that believes "she" came about as a copyist error. A number of current
Protestant translations actually do use "it."
There is a togetherness in Genesis 3:15 that Mary and Jesus are to both have enmity between them and the serpent, and the passage can be fairly understood that the woman crushes the serpent's head through "her" seed. You can see a consistency in this cooperative role of Mary's in the prophecy of Simeon when he prophesies that Jesus will be a savior, and includes Mary in this Passion saying "a sword will pierce your soul too." (
Lk 2:25-35 )
I don't think one should be bothered by statues that show Mary stomping the serpent. If one is well-versed in Marian theology, one knows all her merits are from Christ anyway. In other words, all the good she does, just like you or me, is properly His work. It's kind of like St. Michael the Archangel shown defeating the devil. Does that mean Christ is NOT the devil's defeater? Of course not.
You can also see some
ante-types of Mary in the Old Testament smiting the enemy's head (Jael and Judith), as well as David. See
here for a really good treatment on that. The two women are also typologically told "blessed are you among women": Jael (
Jg 5:24 ) and Judith (
Judith 13:18 ). These women are ante-types of Mary, and these women are shown to have smote the enemy's head in the OT. That gives strength to using the word "she" in Genesis 3:15, or at least renders it reasonable.
You can also see Paul telling the church at Rome how God will crush the serpent under
their feet (
Rm 16:20 ). And Mary is typologically the figure of the Church.