The sinless nature of Mary is evident in the Bible by her being called a virgin.
When man and woman were created, they were created to be virgins and without sin. But God in His wisdom, perceiving the fall of man, created man and woman that they might ‘go forth and multiply’. God can create many men and women without the assistance of mankind, but He made it so that a man and woman join and become one flesh.
Mary was a virgin and never joined with any man but she bore a child, Jesus the Christ our Lord and Savior. And Jesus speaks of the merits of virginity and celibacy in Matthew 19. He did not impose on us any law, because he says “all men cannot receive this saying”, but he mentions that those who are celibate do it for the Kingdom of Heaven.
Virginity is the way of the angels, and in the life to come we will be as the angels who do not marry (Matthew 22:30). But is that saying marriage is a bad thing? No, because the Lord blessed marriage with his presence at the wedding, and marriage is an honorable virtue (Hebrews 13:4), but virginity is the better virtue.
Mary being forever a virgin then possesses the highest of virtues, and not by her own doing but by the grace of God. Elijah possessed such a virtue, and God gave him great power even over kings, and he was taken up to heaven body and soul (2 Kings 2:11), and his spiritual son, Elisha was also a virgin and received from God such great power that even his bones could raise the dead (2 Kings 13:20-21). The three youths in Daniel who were also virgins (Daniel 3:20) were not burned up in the fire, and Daniel himself being a virgin was not able to be eaten by the wild beast.
And then there is of course Jesus The Christ, who is greater than all the angels, being made in the image of man, born of a virgin, who is the glory of virginity, and is the true and perfect virgin.
So there should be no accusations towards Mary in our hearts. For if God, who is the author of life, did all these things, then surely he preserved Mary and she did not sin.
And if we are to take the phrase ‘All’ have sinned as to imply that everyone has sinned, then logically we must say too that a baby has sinned or is capable of it. I’m certain you would not agree with that, so obviously there is something wrong with your interpretation of “All have sinned” as others have already pointed out.
As to Jesus being Mary’s savior, He is everyone’s savior including the prophets and every faithful person under the Law before His coming.