God is not a rapist; he does not act with pure will. (That is the God of Calvinism and Islam.) Rather, He is the God of Logos. The Archangel's words to Mary convey what will happen, not what did already happen. It is only after Mary receives an answer from the Archangel as to how it will be, does she give her fiat voluntatis...
"And he [Gabriel] came to her and said, 'Hail, full of grace, the Lord is with you!' But she was greatly troubled at the saying, and considered in her mind what sort of greeting this might be. And the angel said to her, “Do not be afraid, Mary, for you have found favor with God. And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus. He will be great, and will be called the Son of the Most High; and the Lord God will give to him the throne of his father David, and he will reign over the house of Jacob for ever; and of his kingdom there will be no end.” And Mary said to the angel, “How can this be, since I have no husband?” And the angel said to her, “The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy,the Son of God. And behold, your kinswoman Elizabeth in her old age has also conceived a son; and this is the sixth month with her who was called barren. For with God nothing will be impossible.” And Mary said, "Behold, I am the handmaid of the Lord; let it be to me according to your word.” And the angel departed from her.” (Luke 1:28-38)
As recorded by St. Luke, the Archangel appears to Mary and addresses her not by her name, but rather by a title. ("Full of grace.") What is Mary's response to the Archangel? She asks him a question: "How can this be?" In other words, she brings the Archangel's message under consideration and only when he satisfies her reason does she give her consent, her fiat voluntatis. Mary's rational faculties are not suspended. She is not forced; rather, she is fully engaged as a rational human being.
Continuing on, the Calvinist anti-Logos position is completely destroyed and the Catholic position is affirmed and confirmed in a small detail when St. Luke continues on and describes the name given our Blessed Lord after His birth…
"And at the end of eight days, when he was circumcised, he was called Jesus, the name given by the angel before he was conceived in the womb.” (Luke 2:21)
Did you catch that? "The name given by the angel before he was conceived…” Thus, St. Luke confirms the Incarnation occurred only after Mary’s fiat, not beforehand.
---> Mary knowingly and willingly chose the role God offered her.