“As the Bible teaches”? Are you kidding? First of all Mary surely didn’t realize she was sinless.
Luke 1:29 And when she saw him, she was troubled at his saying, and cast in her mind what manner of salutation this should be.
How could anyone think that a person who is sinless doesn’t know it and others around that person wouldn’t have noticed?
Kecharitomene is a derivative of the word charitoo which we can find the meaning of here. [http://www.biblestudytools.com/search/?q=charitoo&rc=LEX&rc2=LEX+GRK&ps=10&s=References]
Charitoo
to make graceful charming, lovely, agreeable to peruse with grace, compass with favour to honour with blessings
This has been debated over and over and not once can anyone show that kecharitomene ever means sinless. On the other hand let’s look at words that do mean sinless. [http://www.biblestudytools.com/search/?q=sinless&rc=LEX&rc2=LEX+GRK&ps=10&s=References]
Anamartetos
sinless of one who has not sinned of one who cannot sin
Not once used to or about Mary.
Pluno
to wash: with reference to clothing use figuratively of those who by faith so appropriate the results of Christ's expiation as to be regarded by God as pure and sinless
Used about all true believers.
Anamartetos
sinless of one who has not sinned of one who cannot sin
Again, never used about or to Mary.
Hagion
reverend, worthy of veneration of things which on account of some connection with God possess a certain distinction and claim to reverence, as places sacred to God which are not to be profaned of persons whose services God employs, for example, apostles set apart for God, to be as it were, exclusively his services and offerings prepared for God with solemn rite, pure, clean in a moral sense, pure sinless upright holy
In Ephesians 1:6 we can see that God has granted every true believer with grace.
Ephesians 1:6 To the praise of the glory of his grace, wherein he hath made us accepted in the beloved.
Luke 1:28 is rightly translated “highly favored”. To try to make that verse somehow infer that Mary was sinless is deceitful.
From Catholic Answers:
The traditional translation, “full of grace,” is better than the one found in many recent versions of the New Testament, which give something along the lines of “highly favored daughter.” Mary was indeed a highly favored daughter of God, but the Greek implies more than that (and it never mentions the word for “daughter”).
The grace given to Mary is at once permanent and of a unique kind.Kecharitomene is a perfect passive participle of charitoo, meaning “to fill or endow with grace.” Since this term is in the perfect tense, it indicates that Mary was graced in the past but with continuing effects in the present.
So, the grace Mary enjoyed was not a result of the angel’s visit. In fact, Catholics hold, it extended over the whole of her life, from conception onward. She was in a state of sanctifying grace from the first moment of her existence.