I’m no biblical scholar, but I do not believe Mary was asked in advance, giving God permission before she was impregnated. That she happily consented once informed of the situation is in keeping with this article.
The issue is whether this was rape or not, and thus whether Mary's assent was implicit even before being told and expressing it, which is manifestly the case. She counted herself exceedingly blessed, not victimized, thus no rape was involved.
If an angel came up to me and said, I am sending a man to you today with 10 million dollars which will be deposited into your bank account today, and which will grow to an ever greater sum by which to further the work of the kingdom of God,
and to which i then said, "the Lord's will be done," then I would hardly consider myself a victim, seeing as that would be a blessing to me.
But to angry atheists, rationality must too often give place to animosity.