Mary was borne sinless through the Immaculate Conception. However, since all of us are born with Original Sin, she could only have been borne sinless through the Salvation of Jesus Christ. Why couldn't Jesus save his Mother from sin before he "came down from heaven and was made man?" John tells us that Jesus is eternal. All things are possible for God.
Was the mother of Mary also sinless? Surely God would not allow the "Mother of God" to be born from a sinfull womb? And how about Marys mothers mother?
It can go on and on. It just shows the stupidity of such doctrine