First, let me put your mind at ease. The Church teaches that Mary was redeemed by Christ's Passion and death, just like the rest of us. In her case, since she was conceived without sin, she was redeemed in anticipation of Christ's death.
The "Co" in the title, "Co-Redemptrix" is an ambiguous term, in that it has a different historical meaning in the Catholic Church than in our culture today.
The primary meaning is "cooperator." (Paul calls himself a "co-worker with Christ" [1 Cor. 3:9]). The meaning of this term, in a nutshell, is that Mary cooperated with God's plan that she become the Mother of Christ, and in that sense, bringing the Redeemer of Mankind into the world.
For real? She was redeemed *just like the rest of us*? And then you go on to claim she was conceived without sin?
On what planet is that being redeemed *just like the rest of us*? Because nobody I know was ever conceived without sin.
All OT believers were redeemed by their anticipation of Christ's death. That's nothing new or special to Mary.
And Scripture also tells us that ALL have sinned and fall short of the glory of God. ALL is ALL. It doesn't say *All but Mary.*
Mary had sin and needed a savior, by her own admission. If she indeed never had sinned as Catholicism teaches, then she didn't need a savior, in which case, she would have been lying in calling God her savior, which would have made her a sinner.