Most who have difficulty with the doctrine of the Immaculate Conception have never had it properly explained to them. To begin with, Mary always points us to Jesus, and this teaching is ultimately about Jesus.
Jesus has a divine nature and a human nature. The divine nature he has from the Father, through the power of the Holy Spirit. The human nature he has — entirely — from his mother, because he has no human father.
Our salvation is possible because we are allowed to participate in the merits of Christ’s Atonement. The Atonement is an act by which the original disobedience of man is overcome by the perfect obedience of Jesus, the new Adam. Jesus is perfectly obedient to the Father in both his divine and his human natures. In his human nature this is especially hard, because Jesus is a real man, and it’s part of our nature to avoid and resist suffering and death. Nevertheless, Jesus in his human nature gave himself to the plan of his divine Father, without compromise or reservation. It was a perfect gift of self, which is not possible for anyone afflicted by sin (Romans 7:15-23).
Mary comes into the picture because she also is called upon to make a total and unreserved gift of self, in obedience to the Father’s plan (Luke 1:38). It is Mary’s consent that makes possible the perfect union of human and divine natures in Jesus, and therefore makes it possible for Jesus’s sacrifice to be a perfect atonement of infinite merit. As with her divine son, Mary could not have given perfect assent to God’s proposal relayed through the angel, if her mind or flesh had ever been under the bondage of sin. Mary’s sinlessness makes her self-gift of human nature perfect and thus ensures that the Incarnation is genuine and not a hoax.
I hope this helps.
“To begin with, Mary always points us to Jesus, and this teaching is ultimately about Jesus.”
Um. Then why do you reject her counsel and even bother trying to talk to Mary? Take Mary’s advice: Look to Jesus, alone. There is no Co-Mediatrix.