No, she is not in the slightest. Mary is not involved in anyone's salvation other than her own. Period. That error extends the necessary requirement for Christ's human birth into blasphemous hyperbole.
Mary cooperated with God in the redemption of the world and is therefore "Co-Redemptrix" of the human race.
Could Mary have said "no" to God? I very much doubt it. Mary co-redeems no one. To believe so is anti-Scriptural.
No Mary, No Jesus
No Mary, then someone else equally pure of heart to be the mother of the baby Jesus. To even imagine Mary's "cooperation" was required for Christ to be born is ludicrous. God is not beholden to His creation, as much as the RCC would like Him to be.
Calvinism not only robs you of your free will, but we are expected to believe it robs everyone else too.
Good grief.