Our calling is irrevocable. It is determined by the Lord. Had Mary not consented she would have become inconsequential and another would have taken her place.
And Mary is not the mother of God. That’s Roman idolatry. She was the vessel through whom Jesus would come into the earth. Jesus was God in the Spirit, not the flesh.
“The first man Adam became a living being.” The last Adam became a life-giving spirit.
Melchizedek is a precursor of this grace:
“For this Melchizedek… without father, without mother, without genealogy, having neither beginning of days nor end of life, but made like the Son of God, remains a priest continually.”
Jesus was clear:
46 While Jesus was still talking to the crowd, his mother and brothers stood outside, wanting to speak to him.47 Someone told him, “Your mother and brothers are standing outside, wanting to speak to you.”
48 He replied to him, “Who is my mother, and who are my brothers?” 49 Pointing to his disciples, he said, “Here are my mother and my brothers. 50 For whoever does the will of my Father in heaven is my brother and sister and mother.”
I was quoting the sources that upheld the Consent of Mary. As for her being Mother of God, well God always existed, Christ always existed (Colossians 1:16, John 1:3), However, she did carry God Incarnate inside her and was His Mother in that she raised him, fed him, took care of Him and loved Him like a Mother.
It depends on what you mean by Mother, she was a Mother in every sense of word except that she had no hand in creating Jesus, for Jesus was not created, He has always existed with the Father and Holy Spirit.