Jesus had two roles to play.
And Mary was the mother of the person that played both of those roles. Not the mother of the eternal Godhead, but the mother of God in the person of Jesus. This does not make Mary greater than God in any way, shape, or form. It just recognizes that God, while He was with us, was a human being in every way but sin. This includes being the son of a woman.
okay
I recognize that Mary, while she was with us, was a human being in every way; including sin.