Mary sure was privileged to be the mother of the messiah, and birth mother to Jesus, the Son of God, but this does not make her mother of God, because God does not have a mother, for God was never born but always existed, with no beginning and no end.
God-the father of our Lord Jesus, can be compared (in this situation) to the gods of old greeks stories, who came down and had relations with the earthly women. The Demi-gods are the offspring of these gods. Eventhough God almighty never really can down from heaven, he made Mary pregnant through the transver of the life of his only begotten son to the womb of this woman, using his holy spirit. Really a wonderfull miracle!
So after Jesus was born, Mary was no longer, a virgin. Her womb was opened and continued to bare more children for her husband Joseph. (see: Jesus brothers.) This does not mean she is not an important devoted woman. On the contrary! She was the giver of birth to the Messiah, the first to recognize his special role and a life long diciple of the Lord. And as this, a wonderfull example for all women to follow!
(Luke 1:42 and loudly cried out: “Blessed are you among women, and blessed is the fruitage of your womb!)