Many Protestants, and basically all anti-Catholics, think that Catholics hold too high a view of the Blessed Virgin. If, then, they find that we insist that she is saved not on the basis of any intrinsic righteousness of her own, but rather on the basis of the merits of Christ, how much more would it be true that we think the same of ourselves?
The Virgin Mary, who at the message of the angel received the Word of God in her heart and in her body and gave Life to the world, is acknowledged and honored as being truly the Mother of God and Mother of the Redeemer. Redeemed by reason of the merits of her Son and united to Him by a close and indissoluble tie, she is endowed with the high office and dignity of being the Mother of the Son of God, by which account she is also the beloved daughter of the Father and the temple of the Holy Spirit. [Lumen Gentium §53; emphasis added]
It would be ridiculous to suggest that we believe Mary, the Mother of God, to be in need of redemption by Christ, but that we ourselves are saved by what we do! But as we see, the Fathers of Vatican II insist that she was redeemed by Christ, and of course the same applies to us. We cannot save ourselves.