You miss the point....the translation is wrong by Roman Catholicims’s own Catholic Encyclopedia online.
The point is, Gen 3:15 is not a proof-test for the docrine of the Immaculate Conception: please note that the doctrine does not depend on the pronoun she for proof. The pronoun refers to her [Eves] seed.
Here''s the quotation of Genesis 3:15 in New American Bible, Revised Edition (NABRE)
I will put enmity between you and the woman,The word is, at its simplest, "seed," meaning offspring. Here it is construed as a collective singular; hence, the pronoun "they."
and between your offspring and hers;
They will strike at your head,
while you strike at their heel.
The New American Bible Revised Edition (NABRE) is an English-language Catholic Bible translation.
Alternatively, the New Revised Standard Version Catholic Edition (NRSVCE)construes "seed" or "offspring" in an equally legitimate singular sense; hence the pronoun "he":
I will put enmity between you and the woman,
and between your offspring and hers;
he will strike your head,
and you will strike his heel.
I hope you don't mind that I'm agreeing with you.