Inimicitias ponam inter te et mulierem et semen tuum et semen illius ipsa conteret caput tuum et tu insidiaberis calcaneo eius.The word ipsa translates an epicene Hebrew personal pronoun: one that has only one form to denote either male or female. It can legitimately be translated either as "he", "she", or "it." In one place, St Jerome quoted the Vetus Latina version which gives ipse. (Lib. Quaest. Heb. in Gen. PL 23.943) and this has been taken as evidence that the reading ipsa must be the result of a copyist's error.
(I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel.)
This assumes that Jerome continued with the Vetus Latina translation "ipse" which could easily be corrupted by a copyist to "ipsa." However, "ipse" does not agree with either mulier or semen. Would not Jerome, have given ipsum which would be an acceptable rendering of the epicene pronoun in Hebrew and would agree with semen? Of course, that would make it much less likely that a copyist would corrupt the text to read ipsa. Perhaps St Jerome did write ipsa after all?
In his article for the New Catholic Commentary (1969), Bruce Vawter attributes the ipsa reading to Ambrose who, he says, was dependent on Philo. It may also be the case that St Jerome had access to sources and information that are no longer available to us. But this idea has been unfashionable in recent years.
Indeed, the Catechism of the Catholic Church does seem to take up a position on the question:
"After his fall, man was not abandoned by God. On the contrary, God calls him and in a mysterious way heralds the coming victory over evil and his restoration from his fall. This passage in Genesis is called the Protoevangelium ("first gospel"): the first announcement of the Messiah and Redeemer, of a battle between the serpent and the Woman, and of the final victory of a descendant of hers."(For the passage to announce a victory of "a descendant of hers" rather than simply her victory, we would need the reading ipse or ipsum.)
So the general consensus seems to be that "ipsa" must be rejected although I cannot see that the case has been made with certainty. What cannot be rejected, however, is the Marian interpretation of Genesis 3.15 which is supported by the Fathers of the Church and by the Magisterium.
Pius IX in Ineffabilis Deus (proclaiming the dogma of the Immaculate Conception) said that in this verse, the Virgin Mary was prophetically indicated. Pius XII in Munificentissimus Deus (proclaiming the dogma of the Assumption) said (n.39)
"We must remember especially that, since the second century, the Virgin Mary has been designated by the holy Fathers as the new Eve, who, although subject to the new Adam, is most intimately associated with him in that struggle against the infernal foe which, as foretold in the protoevangelium, would finally result in that most complete victory over the sin and death which are always mentioned together in the writings of the Apostle of the Gentiles."In Redemptoris Mater, Pope John Paul II said of the divine plan of salvation:
"It includes everyone, but it reserves a special place for the "woman" who is the Mother of him to whom the Father has entrusted the work of salvation. As the Second Vatican Council says, "she is already prophetically foreshadowed in that promise made to our first parents after their fall into sin" - according to the Book of Genesis (cf. 3:15)"Pope John Paul's reference is to Lumen Gentium n.55 which says:
"The books of the Old Testament describe the history of salvation, by which the coming of Christ into the world was slowly prepared. These earliest documents, as they are read in the Church and are understood in the light of a further and full revelation, bring the figure of the woman, Mother of the Redeemer, into a gradually clearer light. When it is looked at in this way, she is already prophetically foreshadowed in the promise of victory over the serpent which was given to our first parents after their fall into sin."This passage gives you the opportuity to have fun if anyone tells you that Genesis 3.15 does not refer to Mary. You can reply "Vatican II says it does."
The above passages do not necessarily take a position on the question of ipse/ipsa/ipsum. Mary is foreshadowed in any case – she is the mother of the offspring or seed referred to. In my opinion, we are entitled to accept the long-standing tradition represented in many statues and pictures showing the serpent crushed under the heel of Mary.