Free from all sin by a gift from God

Obviously it was not Mary who exempted herself from original sin: this was a free gift she received from God. "The Almighty has done wonderful things for me," Mary sang in the hymn of the Magnificat (Luke 1:49). Why would it be impossible for God to do for Mary what he had done for Eve? Before original sin happened, Eve was without any sin! Who are we to tell God what he can or cannot do!

The Scriptures talk about this exceptional gift of God to the Virgin Mary in several places. First, the Archangel Gabriel addresses Mary with these words: "Rejoice, Thou" (or "I greet you," because in Greek a greeting is expressed by the expression Kairé, i.e. “rejoice”). Then Gabriel says "Kekaritomene" which means "who has been filled with grace." What does that mean? There is no other occasion in the Bible where an Angel of God greets a man or a woman in this way, so we shouldn’t interpret it simply as "you are very fortunate."

The exceptional grace given by God to Mary is the ability to say a perfectly free "yes"!

(From a talk about Mary and the Protestants)

Source: Mary’s Perfect Holiness