When we say "Hail Mary full of grace" we quote the angel sent to gain Mary's consent to made Mother of God. Her submission "behold the handmaid of the Lord" is a model of Christian faith.
>>”Hail Mary full of grace”<<
And surprise!
That is scripture!
That statement in and of itself is quite remarkable. I may be wrong about this, but I'd be hard-pressed to think of any other place in the New Testament where an angel (the archangel Gabriel, no less) offered a salutation of this kind to a human being.
Go back and look carefully at the salutation of the angel Gabriel. This salutation itself ("Hail, full of grace!") makes a very clear statement about the unique nature of Mary. In general terms, grace is the means by which humans are granted salvation by God and saved from the effects of original sin. Grace by definition is the result of Christ's Redemptive mission, and Old Testament figures did not enjoy any fruits of this Redemption while they lived on this earth (even those who were greatly favored by God).
In this context, this statement by Gabriel that Mary was "full of grace" can be seen as a remarkable acknowlegement that she had already been given the benefit of Christ's Redemption before He died on the cross and rose from the dead.