Proposition 1: Mary is the mother of Jesus.
Proposition 2: Jesus is God.
Therefore Mary is the mother of God.
If you don’t agree with the conclusion, which of the two propositions do you reject?
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.