Dear Charles:

Sorry for the delay in responding.

It is duplicitous for Protestants to make this claim. Martin Luther added words to the text of St. Paul. Luther, in his abject arrogance, added the word "alone" to the passage in Romans 3:28 in his German translation, in addition to ripping our seven books from the Old Testament and wanting to rip out several books from the New Testament.

Luther, in fact, was confronted at the time on why he had added the word "alone" to Romans 3:28. His response is very revealing. To the criticism of adding the word "alone" to Romans 3:28 Martin Luther replied:

"You tell me what a great fuss the Papists are making because the word 'alone' is not in the text of Paul. If your Papist makes such an unnecessary row about the word 'alone,' say right out to him: 'Dr. Martin Luther will have it so,' and say: 'Papist and asses are one and the same thing.' I will have it so, and I order it to be so, and my will is reason enough. I know very well that the word 'alone' is not in the Latin or the Greek text, and it was not necessary for the Papists to teach me that. It is true those letters are not in it, which letters the jackasses look at, as a cow stares at a new gate...It shall remain in my New Testament, and if all the Popish donkeys were to get mad and beside themselves, they will not get it out."

Thus sayeth the "humble" Martin Luther.

The translations of the Bible by Protestants contain many translation decisions that favor their own theologies. This is not unusual.

For instance, the rendering of John 3:16 in a literal translation, such as the Catholic Douay-Rheims Bible (DRC), would say, "For God so loved the world, as to give his only begotten Son; that whosoever believeth in him, may not perish, but may have life everlasting." However, a popular dynamic Protestant translation, the New International Version (NIV), quotes John 3:16 as, "For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life."Note how the NIV omits the word "may" before the phrase "have life everlasting." Clearly, Protestant bias, whether inadvertent or not, has crept into the NIV text. Protestants commonly believe that salvation is dependent only on having "faith" in God, without consideration of works of righteousness. The skewed translation of the dynamic NIV alludes to the Protestant belief that faith in Christ is all that is needed for salvation; a view which Catholic doctrine rejects. (Source: What Bible Should I Use? by S.M. Miranda)

In addition, many Protestants say the Bible says that the Catholic Church is the "whore of Babylon" even though there is no such reference. Such Protestants like to be scrupulous to the words in the text, yet the text does not have the words "Catholic Church." They are making in inference based upon their biased doctrine, not based upon the text.

Now as to your question, quoting from the Navarre Bible Commentary:

The punishment God imposes on the serpent includes confrontation between woman and the serpent, between mankind and evil, with the promise that man will come out on top. That is why this passage is called the "proto-gospel": it is the first announcement to mankind of the good news of the Redeemer-Messiah. Clearly, a bruise to the head is deadly, whereas a bruise to the heel is curable. ...

Victory over the devil will be brought about by a descendent of the woman, the Messiah. The Church has always read these verses as being messianic, referring to Jesus Christ; and is seen in the woman the mother of the promised Saviour; the Virgin Mary is the new Eve. "The 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 a woman, mother of the Redeemer, into a gradually clearer light. Considered in this light, 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. Hence not a few of the early Fathers gladly assert with Irenaeus in their preaching: 'the knot of Eve's disobedience was united by Mary's obedience: what the virgin Eve bound through her disbelief, Mary loosened by her faith'" (St. Irenaeus, Adv. haer. 3, 22, 4)

...

So, woman is going to have a key role in that victory over the devil. In his Latin translation of the Bible, the Vulgate, St. Jerome in fact reads the relevant passage as "she [the woman] shall bruise your head". That woman is the Blessed Virgin, the new Eve and the mother of the Redeemer, who shares (by anticipation and pre-eminently) in the victory of her Son. Sin never left its mark on her, and the Church proclaims her as the Immaculate Conception.

Now I suppose Protestants can say that St. Jerome changed "he' to "she" in this passage, but there is a very big difference in this as compared to what Protestants did to John 3:16 in the New International Version and may other of their Bibles. In leaving out the word "may" they change doctrine. The Catholic Church does not that.

Here, the Catholic Church affirms that this passage refers to Jesus Christ. In light of fuller understanding of the Holy Spirit, St. Jerome understands that Mary crushes the head of Satan because it is through her that this will happen by her Son, which is her seed. This does not change the meaning of the passage as does the Protestant translations of John 3:16.

An imperfect analogy of this is that the accomplishes of the child are credited to the parents. This was certainly true with the Kings of old who were given credit for the accomplishment of their sons. Even today we do this to some extent as it is a credit to the parents for raising a child who made such accomplishments.

I hope this helps.

God Bless,
Bro. Ignatius Mary