All Christians will agree that there is at least one person who never sinned and that is our Lord and Savior. Being an exception means that there may be other possibilities of exceptions although we can agree that the circumstances of our Savior are unique being fully man and fully God. No other person future or past can make such a claim. As you know the Bible says that the blessed mother is "full" of God's grace at the Annunciation. We believe that God had prepared her for that moment of saying yes to be the God bearer. The womb that bore and nurtured our Lord is the Ark of the New Covenant which is Christ our Lord. God cannot dwell within sin so the blessed mother was saved by God's grace before she was even conceived in the womb immaculately. She was in need of a Savior as we all are and our Lord provided for her salvation and indeed her sanctity even before her conception. Being and remaining full of grace means that the blessed mother of God never sinned but would have been tempted to sin as the new Eve just as the original Eve was tempted. But just as her Son withstood temptation, her grace was so great that she was able to overcome all temptation.
Just for the record, the Bible also says that St. John the Baptist was saved from original sin but he was saved at birth and not conception. The blessed mother was unique in her immaculate conception. God bless!