Of course Mary was baptized and received the gift of the Spirit, as every Christian was. Although unlike other Christians, she had a particularly unique indwelling of the Spirit before that, at the annunciation. Until that point, she did the best with what she had available to her, much like the holy and righteous OT saints that came before her, along with John the Baptist. It is indeed our tradition that Mary was blameless in the eyes of God, as scripture attests to the same regarding Zechariah and Elizabeth: "Both of them were upright in the sight of God, observing all the Lord's commandments and regulations blamelessly." (Lk. 1:6) Considering what Jesus had to say about John, to say that he did not attain such a high state of perfection by God's grace is indeed Pelagianism.
Baptism remits sins and unites us to Christ through the power of the Spirit. Uniting ourselves with Christ is the only means to salvation.