What proof do you have of her not sinning?
You are stating she's an exception to the rule.
Romans 3:21-25 But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: for all have sinned and fall short of the glory of God, and are justified by his grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith.
Now, since you are claiming an exception to the rule, then you need to prove it.
Show us plain and clear Scripture that says "Mary, without sin".
The biblical view of Mary is that she has been specially set apart by God in the order of grace. Elizabeth, filled with the Holy Spirit, was one of the first to affirm this when she proclaimed Mary’s blessedness upon her visitation:
And when Elizabeth heard the greeting of Mary, the babe leaped in her womb; and Elizabeth was filled with the Holy Spirit and she exclaimed with a loud cry, “Blessed are you among women, and blessed is the fruit of your womb! (Luke 1: 41-42).
One reason that the Virgin Mary is set apart from all other women is because of the weight of her “yes” to God’s plan—and because of God’s “yes” to her. Following her consent to bear the Christ child in her womb, her flesh was united with the body of Christ in the most literal sense. No other woman will ever experience this kind of union with Christ, this mother-with-child communion. Clearly, by this fact alone, Mary is blessed among women.
Steeped in the writings of the early Church Fathers and drawing from their reflections on Mary, the convert Bl. John Henry Newman fittingly called the mother of Jesus “the daughter of Eve unfallen.” Indeed the earliest Church Fathers hinted at Mary’s sinlessness in their writings when they alluded to Mary, implicitly and explicitly, as the second or new Eve. St. Irenaeus, for example, writes in the second century that “the knot of Eve’s disobedience was loosed by the obedience of Mary. What the virgin Eve had bound in unbelief, the Virgin Mary loosed through faith” (Against Heresies 3:22:24).
The later Church Fathers conveyed the blessedness of Mary even more explicitly. Consider the words of St. Ephrem in the fourth century:
You alone and your Mother are more beautiful than any others, for there is no blemish in you nor any stains upon your Mother. Who of my children can compare in beauty to these? (Nisibene Hymns 27:8).
Even Martin Luther believed that Mary had received special graces from God, professing in a 1527 sermon:
It is a sweet and pious belief that the infusion of Mary’s soul was effected without original sin; so that in the very infusion of her soul she was also purified from original sin and adorned with God’s gifts, receiving a pure soul (On the Day of the Conception of the Mother of God).
Of course, this recognition began with the biblically unique greeting of the angel Gabriel: “Hail, full of grace” (Luke 1:28). He greeted Mary with a title—and an angel never speaks anything but exactly what God wants him to speak. This explains why Mary in all her humility “was greatly troubled at the saying, and considered in her mind what sort of greeting this might be” (Luke 1:29).
At the very least we should remember, as St. Ambrose did in his commentary on holy virginity, that Mary’s life “is like a mirror reflecting the face of chastity and the form of virtue.” We have ample reason to believe that Mary was a perfect model of obedience and humility, and so we can do no better than to reflect on her life, though but for the grace of God she would have been conceived in sin and unfit to be Christ’s mother and ours. Nobody has understood our dependence on God’s grace greater than she whose sweet voice proclaimed in the home of Elizabeth:
My soul magnifies the Lord,
and my spirit rejoices in God my Savior,
for he has regarded the low estate of his handmaiden.
For behold, henceforth all generations will call me
blessed (Luke 1:47-48).
https://www.catholic.com/magazine/online-edition/our-mothers-singular-grace