Don't know much about "the Magnificant". Clearly, Old Testament believers (Jews and some early non-Jews) had saving faith and Hebrews chapter 11 records it from a post-crucifixion perspective. I don't believe that between His birth and crucifixion that the Lord held a moratorium on saving souls.
Most Biblical scholars believe the faith these OT saints had was one of partial understanding but solid faith in the Messiah yet to be revealed. None of them were worthy of God's grace in and of themselves.
Mary may have been saved as was Abraham or she may have been saved as we are. But either way- she had to have come to realize her sinful nature in light of her understanding of Holy God and trust Him in faith to deliver her from her sin.
It's the Magnificat. Are you saying you don't know what it is or that you have never read it?