Calling Mary Coredemptrix does not include making her divine or that she died for our sins.
It implies both the Divinity of Mary & her Atoning Death. Not to mention her Infinite Merits: it cannot be true unless she is God. And some people think she is. 
Redemption cannot be the work of two - & the idea makes a mockery of the Biblical type of Christ the Redeemer in Isa. 63 (repeated with additions in Rev. 19). In those texts, He is blood-spattered from treading the “wine-press of the wrath of God” - Mary never did that. She is not holy enough, gracious enough. If she cannot look sin in the face & suffer the full alienation of man from God, she may be a beneficiary of the Death of Christ, but she cannot in any sense be a redeemer or mediator. She may be on our side - but Jesus Christ our Glorious & Unique Redeemer is on His Father’s side
and on ours, wholly, fully, equally, “simultaneously”. The notion of co-redemption eats away at all the Glory & Work & Teaching of Christ - it says His Redeeming work is divided with another, & her a mere creature. A divided Mediator implies a divided Christ - & what good is such a Christ to us ? None, that’s how much.
Yes, Christ is our sole mediator–of Justice. Mary is a mediator of grace. Perfectly sound theology.
Then He is not our sole mediator, & St. Paul was ludicrously mistaken - for he did not know He has a colleague. And one who can make up for the deficiencies in His Work; who, even worse, is better than He. The blasphemy of this is beyond words. It falsifies the NT teaching on the mediation of Christ, by giving a mere mortal what is possible to Him alone. He is either Our Mediator in every respect - or He is not Our Mediator at all. There is no possibility of compromise here.
Since there are two mediators, & not one - despite St.Paul’s assertion to the contrary - it follows that the Bible contains a doctrinal error; & a serious one. This collides with the dogma of total Biblical inerrancy. Such confusion is inevotable when a lie is introduced into Chuirch teaching
This division of the Mediation of Christ is not Biblical - it’s a 10th century idea, of Eastern origin; the West could have done without it
Its only justification is that it teaches men - has taught them - that Christ is an angry Judge from Whom they should flee, that they may find protection from Him by appealing to the mercy of His mother. This is a denial of the infinite Mercy of Christ, an exaltation to parity with Him of a mere creature, & a denial of the NT: it is not a Christian idea.
Mary has, can have, could have, no grace whatever if Her Creator were not the Gracious Author of all grace. It is Christ Who is the Source of all grace in the Church, for He is the Head of it. Mary is not, cannot be, gracious in the slightest, except as a grace: a totally free Divine gift to which she has & can have not the faintest shadow of any claim at all. So the foundation of this “two kingdoms” theory (as it is known in its more familiar form) - the kingdom of justice, & the kingdom of grace - is rotten. To divide the kingdom of Christ is anti-Biblical, anti-Christian, & anti-Catholic. An error a thousand years old does not become a truth merely by being old.
Yes, God has already elevated her and does not need us to acomplish what God has already done, but that does not mean we cannot formally acknowledge true aspects of that elevation. The Church is not throwing darts at a board and making this stuff up out of thin air.
Scott
