"Co" in co-redeemer, co-Mediatrix, etc. is Collaborator. Mary "assisted" in our redemption and she assists in our mediation with Christ.
This context does not give Mary equal status with Christ, or usurp Christ in anyway. She, rather, merely cooperated and collaborated with Christ.
In a sense we, too, are co-mediators every time we pray for someone. We are offering intercession/mediation for our friend when we pray for them. This does not make us God or equal with God, it only means that we are cooperating with the economy of God when he asked us to be a family and pray for each other.
In terms of Mary as co-redeemer, she did in fact, cooperate in the redemption. When she made her fiat to accept God's will for her to bear the Christ Child she was cooperating in the redemption of mankind for it was through her that the Redeemer came into the world.
The solution to problems like this is not suppression but education.
"co" just simply does NOT mean "equal to".
As for Judas, no he was NOT co-redeemer. Jesus could have been crucified without Judas' help. Jesus could have been arrested at any time whenever he was in public. In fact, Jesus mentions this in the Garden when he was arrested. Judas happened to be the instrument of Jesus' arrest, but was not necessary for Jesus' arrest. This is different than with Mary...
Mary's role was not incidental but REQUIRED. Jesus, to be incarnated, HAD to be born of a woman, otherwise he would not be human and thus could not be the redeemer.
Mary's collaboration was required; Judas' participation was not, but was incidental.
At this time the theory of co-redeemer is not Church dogma, and is not binding for belief by the faithful. But the concept should not wrinkle our shirts if we understand the nature of her role in the incarnation and the true meaning of "co".