If so, she admitted her lack of sinlessness. As the church father Tertullian explained:
Having considered God's generosity, we pray next for His indulgence. For, of what benefit is food if, in reality, we are bent on it like a bull on his victim? Our Lord knew that He alone was without sin. Therefore, He taught us to say in prayer: 'Forgive us our trespasses.' A prayer for pardon is an acknowledgment of sin, since one who asks for pardon confesses his guilt. Thus, too, repentance is shown to be acceptable to God, because God wills this rather than the death of the sinner.Tertullian, On Prayer, Chapter 7
And Tertullian is right: no one was without sin, save God alone. Mary never prayed the Rosary (the very idea of her praying to herself is absurd), but we have no reason to suppose that she did not pray the Lord's prayer, or prayed it incompletely. Indeed, Mary acknowledged that she needed a saviour:
46 And Mary said, My soul doth magnify the Lord, 47 And my spirit hath rejoiced in God my Saviour.
So, by all means, do follow the greatly blessed mother of our Lord, to the Lord. Repent of your sins and place all your trust for eternal life in him alone, and you will be saved.