This was NOT what I was taught, and I grew up in a fairly conservative RCC parish.
The way I understand it is that Mary was human, born human with all the human frailities instilled in her as a descendent of Eve. YET, because of her love of God, and her purity of spirit and soul, she found favor with God and God asked her to become the Mother of the Word of God : Christ, God Incarnat, BOTH Man and God. That is all. It was HER free will to say yes or no.
To ascribe divinity to Mary is to say that she was 'pre-made' for the position, and God just went through the motions. I find that idea very offensive, and is one reason why I left the RCC.
Jesus' conception is called the Miraculous Conception because he was conceived without a human father. Being conceived by the Holy Spirit and the Virgin Mary, Jesus received both Divinity and humanity by his Miraculous Conception.
By her Immaculate Conception, and her Fiat Mary becomes the highest human being that ever lived who in nature was human alone. Christ being both God and man is more than human: he is both human and divine. His mother is God's creature; he is God's son. This makes all the difference in the world.