If Mary was sinless, she could not have needed redemption! Yet is not Christ the Redeemer of every child of Adam?

In so far as the sin of Adam involved the whole human race in condemnation Mary needed redeeming. But there are two ways of redeeming. God could allow one to be born in sin and then purify the soul by subsequent application of the merits of Christ, or He could, by an anticipation of the merits of Christ, exempt a soul from any actual contraction of original sin. Thus He exempted Mary from any actual inheritance of the sin, and she owes her exemption to the anticipated merits of Christ. In other words, she was redeemed by Christ by prevention rather than by subsequent purification.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty