Youcat commented through CCC - Question n. 84 - Part I.

YOUCAT Question n. 84 - Part I. Was Mary only an instrument of God?

(Youcat answer) Mary was more than a merely passive instrument of God. The Incarnation of God took place through her active consent as well.       

A deepening through CCC

(CCC 508) From among the descendants of Eve, God chose the Virgin Mary to be the mother of his Son. "Full of grace", Mary is "the most excellent fruit of redemption" (SC 103): from the first instant of her conception, she was totally preserved from the stain of original sin and she remained pure from all personal sin throughout her life. 508

Reflecting and meditating   

(Youcat comment) When the angel told her that she would bear “the Son of God”, Mary replied, “Let it be to me according to your word” (Lk 1:38). The redemption of mankind by Jesus Christ thus begins with a request by God and the free consent of a human being—and a pregnancy before Mary was married to Joseph. By such an unusual path Mary became for us the “Gate of Salvation”.   

(CCC Comment)

(CCC 493) The Fathers of the Eastern tradition call the Mother of God "the All-Holy" (Panagia), and celebrate her as "free from any stain of sin, as though fashioned by the Holy Spirit and formed as a new creature" (LG 56). By the grace of God Mary remained free of every personal sin her whole life long. (CCC 509) Mary is truly "Mother of God" since she is the mother of the eternal Son of God made man, who is God himself.    

(This question: Was Mary only an instrument of God? is continued)