No, this claim is itself a myth. Mariology had nothing to do with Jerome's rendering of Genesis 3:15:
The Vulgate translation of Genesis 3:15, or what is traditionally called the protoevangelium (first Gospel, on account of it being the first good news of the Savior to come) is even more clear on the Immaculate Conception. She shall crush thy head and thou shalt lie in wait for her heel. Her heel would never be under the power of the devil. He would lie in wait for the crushing from the one creature over whom he had no power. The parallelism of the couplet loses its relation of the woman and she in opposition to thy head and the serpent waiting for her heel when you translate the Hebrew as masculine in the second part. Saint Jerome had the extant Hebrew and Syrian codices before him as he did his translating in the late fourth and early fifth centuries. He was a master of the inspired languages, Greek and Hebrew, the greatest linguist in the Latin world. He would know, if not from examining the variant codices in existence in his time, then from the rabbis themselves who taught him, that the Hebrew pronoun in this text needed a feminine gender. Although he actually preferred, at first, to give the verse a masculine pronoun, he ended up choosing otherwise because the feminine she shall crush was the more common acceptance among the Latin fathers. In the East, Saint Ephrem, the Syrian doctor, who knew Hebrew (his native tongue, Syriac, was very close to Aramaic), also gave the couplet a feminine translation.
There is an exhaustive study by the late scholar, Brother Thomas Mary Sennott, in a book he wrote on this very subject, The Woman of Genesis, in which he proves the case for the better accuracy of the Vulgate translation. . .
To conclude. In the protoevangelium, the Greek Septuagint has autos as the subject for the second couplet, autos is the masculine nominative pronoun he. Jerome knew that, but he still rendered the subject feminine by using ipsa in his Latin translation of the Genesis text, basing that choice on the older Latin texts in circulation in the West, or, quite possibly, on what the rabbis of the fourth century told him were the correct vowels belonging to the Hebrew pronoun in question.
You will find it notes there is no direct Scriptural support for this issue and that the translation of Gen 3:15 by Jerome cannot be defended.
I'll get the exact quote later.
Here, you err.
What is being discussed was not Jerome's original rendering, but instead was later alteration. Whether it have been merely later copy(ing) error, or something more deliberate, is anyone's guess.
Check out the latest, now corrected Vatican (Latin) version.