Two natures and Mary was the mother of.....one of them. She was not the mother of God. Bottom line: if she was the mother of the divine, then she preceeded the divine, was the source or beginning of the divine. That is untrue.
Interesting discussion.
Since the birth of Jesus is a singular unique event and a supernatural one at that our earthly language probably does not contain an adequate vocabulary to describe it.
As to your comment, I your child is the product of two others, namely you and your husband, and carries traits of each of you, do you say "I am the mother of his blue eyes and blond hair and my husband is the father of his large muscles and above average height."?
Or are you the mother of the whole child?
Is not then Mary the mother of Jesus in total - even of the nature that she had no part in?