Your answer to both questions is slightly contradictory, in that for the first answer, none of us would need a savior for precisely the same reason that the Blessed Mother does in your second answer. I would say that for the first question the reason that the Blessed Mother is given this grace distinct from us, is because it shows us first a greater understanding of who Christ is in relation to us, and by presenting Christ in the pure vessel of the Blessed Mother, he shows us that He is the high priest, the Word of God, and the Bread of Life. Just as the ark of the covenant (think Indiana Jones) contained the ten commandments or the Word of God on the stone tablets, the staff of Aaron, and an urn containing the mysterious Manna from Heaven, the New Ark contains the fulfillment of those types–God in the flesh, so to speak. The second reason is because it shows us a greater understanding of who Mary is in relation to Christ. She is the Ark of the New Covenant. In ancient Isreal, there was simply nothing holier than this one vessel, the Ark of the Covenqnt. It was where God himself resided by overshadowing the Ark, just as the Archangel Gabriel foretold the overshadowing of Mary by the Holy Spirit, or as David exclaimed in 2 Samuel, “how is it that the Ark should come unto me,” Elizabeth in the Gospel of Luke exclaimed, “how is it that the Mother of my Lord should come unto me”. Even the same Greek word for “exclaimed” is used in both 2 Samuel and Luke, and is used only four other times (anophoneo) in the old testament and in each case was used in praise and shouting before the Ark of the Covenant by the Levites, or priestly class. It is worth noting that Elizabeth in her “shouting praise” (once again, anophoneo) of Mary is, in fact, a Levite as well.
For your second question, the answer is yes of course, since Mary herself exclaims as much from the Magnificat, taken from the gospel of Luke, “my spirit rejoices in God my Savior”. John Dun Scotus, a catholic theologian and philosopher from the 13th century was one the first to develop the theology that while Mary was without sin, she would still be in need of a savior by explaining that while one might be saved from a pit after having fallen in, Mary singularly was saved from the pit before having fallen in. In both cases, there is need of a Savior, but only the latter was free from the pit or “stain” of sin.
