It does not seem to be supported by your own Roman Catholic catechism. The doctrine of the Immaculate Conception. "The Gospel According to Rome". James G. McCarthy. Of Mary. "...in the first instant of her conception.. was preserved free from all stain of original sin..." Now that would be your Catechism paragraph [491]. - Pope Pius IX, Ineffabilis Deus.
And then there is the Annunciation, the angel Gabriel's announcement of Christ's incarnation to Mary: "Hail,full of grace, the Lord is with thee: blessed art thou among women" (Luke 1:28 Douay Rheims), Catechism 490-491. This says the Church, reveals that Mary "was never subject to the curse"* and that she was "immune from all sin, personal or inherited."**
* -Pope Pius IX, Ineffabilis Deus. **-Pope Pius X11, Mediator Dei. no. 73.
So just exactly was she in need of a Savior, if she had no sin to be saved from? And if this is true, why teach she had no sin, personal or inherited?
This subject is quite deep and could take much time to wade through but in short....
Mary is called the new Eve and the Ark of the New Covenant.
Eve was created by God without sin. Mary is saved from sin by God at the moment of her creation in the womb(conception).
The Ark of the Covenant was created to hold the Word of God. It was made as specified by God for this and once it held the Word it could not be touched by any human.
God told Jeremiah, “Before I created you in the womb, I selected you; Before you were born, I consecrated you”
Elizabeth tells Mary, “As soon as the sound of your greeting reached my ears, the baby in my womb leaped for joy.”
So, we see that God works even in babies yet in the womb. And that God sets specific attributes and makes preparation for those who He uses to do His will.
The Church teaches that Mary was preserved from the stain of original sin at the moment of her conception. By the very fact that she had to be preserved, we know that she had to have a Savior.