Mary was preserved from sin by the grace of Christ. Thus, she speaks rightly when she says in Luke 1:46:
“And Mary said, ‘My soul magnifies the Lord, and my spirit rejoices in God my Saviour.’”
For, even though she had never sinned, if it were not for the grace of Christ, she would not have been preserved, and thus she would not have been saved.
In Luke 1:28, the angel greets Mary:
“Hail, Full of Grace, the Lord is with thee.”
First, note that the angel does not greet Mary with her name. What this implies is that “Full of Grace” is a title, or perhaps even Mary’s true name (as is in harmony with the rest of Scripture when God gives a new name to those He tasks with a particular mission or blessing).
Second, the word that is translated into “Full of Grace” is the Greek word Kecharitomene. The root word here is charito, which may be translated as “grace” or “favor.” The reason for the double-meaning is that it might be understood that if you favor one, you will grace him, or if you’ve graced one, it’s because you favor him. So the two meanings go hand-in-hand.
The prefix ke indicates this word is in the perfect tense. As shown here: en.wikipedia.org/wiki/Perfect_(grammar), the perfect tense, in Greek (and English) refers to something having been completed in the past, with reference to present consequences of that past action. So, with respect to Mary’s grace or favor, this is an event that was completed in the past with reference to Mary in the present moment.
The suffix mene indicates this word is a passive participle. As shown here: thefreedictionary.com/Passive+participle, a participle is a word that can act independently as an adjective, or it can be used with an auxiliary verb to indicate tense, aspect or voice. That kecharitomene is a passive participle, indicates this is something happening to the noun, as opposed to something being done by the noun.
If taken as an adjective, it may be translated as “Favored (or Graced) [one])” (one would be implied, since there’s no noun the adjective is modifying). If taken with an auxiliary verb, it may be translated as “[You who] have been Graced (or Favored).” However, given that this is in the perfect tense, we know the past action is complete and this action carries through to the present. Thus, you may translate it as either “Completely (fully/wholly/entirely/perfectly) Graced (or Favored) [one, who is as such even now]” or “[You who] have been, and continue to be,] Completely Graced.”
The bottom line of what this word means is this: God *completed *His action of saving grace upon Mary in the past, and that action carries forward to the present (i.e., she continues to be fully graced by God). This is who Mary is, the one who God has graced more than any other, fully and completely, from her creation to eternity. This is her title, her true name: Kecharitomene. She still fulfills Ephesians 5, because it was and is God who sanctifies her.