The OP fails to take into account the precise meaning of “original sin”:
Although it is proper to each individual,295 **original sin does not have the character of a personal fault **in any of Adam’s descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called “concupiscence”. Baptism, by imparting the life of Christ’s grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle. **
The unique vocation of Mary to be the mother of the Saviour surely entitles her to have a unique spiritual status.
The doctrine of original sin, closely connected with that of redemption by Christ, provides lucid discernment of man’s situation and activity in the world. By our first parents’ sin, the devil has acquired a certain domination over man, even though man remains free. Original sin entails “captivity under the power of him who thenceforth had the power of death, that is, the devil”.298 Ignorance of the fact that **man has a wounded nature inclined to evil **gives rise to serious errors in the areas of education, politics, social action299 and morals. **
It is logical that the woman who consented to be the mother of the Saviour should be purified** in advance **by the suffering she shared with her Son when He was scourged and crucified.
408 The consequences of original sin and of all men’s personal sins put the world as a whole in the sinful condition aptly described in St. John’s expression, “the sin of the world”.300 This expression can also refer to the negative influence exerted on people by communal situations and social structures that are the fruit of men’s sins.301
It is hardly surprising that the woman who was bearing Christ in her womb wasn’t subject to that influence.
409 This dramatic situation of "the whole world [which] is in the power of the evil one"302 makes man’s life a battle:
The whole of man’s history has been the story of dour combat with the powers of evil, stretching, so our Lord tells us, from the very dawn of history until the last day. Finding himself in the midst of the battlefield man has to struggle to do what is right, and it is at great cost to himself, and aided by God’s grace, that he succeeds in achieving his own inner integrity.303**Mary was tempted - especially when she became aware of the horrifying ordeal that lay ahead but she was united to Jesus spiritually as well as maternally. In the words of John Keats her unselfish love gave her “negative capability”. She identified herself with Him totally, fulfilling His prayer for all of us:
20 Neither pray I for these alone, but for them also which shall believe on me through their word;
21 That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me.
22 And the glory which thou gavest me I have given them; that they may be one, even as we are one:
23I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.
24 Father, I will that they also, whom thou hast given me, be with me where I am; that they may behold my glory, which thou hast given me: for thou lovedst me before the foundation of the world.
25 O righteous Father, the world hath not known thee: but I have known thee, and these have known that thou hast sent me.
26 And I have declared unto them thy name, and will declare it: that the love wherewith thou hast loved me may be in them, and I in them.