Mary is not the mother of God, she was the vessel that carried YHWH’s Earthly incarnation into the world.
That is obviously why Christ said so many times that all the believers that surrounded him were his mother and brothers. His blood brothers were no more to him than any other.
You didn’t answer the question. It is a very simple and sound syllogism. If you do not agree with the conclusion, then which of the two premises do you disagree with?