All of God’s servants and children who give their lives to God are therefore co-redemptrix? Are we not all called to portray God in our lives and bring others to redemption? Bearing the Son of God did not guarantee Mary’s salvation. It was the gift of faith from God in that baby as Savior that saved Mary.
The decision of Christ to choose Mary, from her conception onwards is what kept her from sinning, and granted her salvation. This is different from anyone else.