I'm opposed to the definition of Mary as Co-Redemptrix. It is not scriptural, and runs the risk of elevating Mary to a co-equal status with Her Son.
Mary is "Co-Redemptrix" in the sense that her cooperation with God, her "fiat," brought our Savior into the world. In no way is the title meant to elevate Mary to the Godhead.
Since the prefix "co" is often interpreted as "co-equal," it would be very easy to misinterpret this title and assume that the doctrine "elevates Mary to a co-equal status with her Son."
The pope has refused to promulgate this dogma for this pastoral reason.