I said "...Come on, God knew what Mary was going to say. It is a figure of speech to say that the angel "waited" for Mary's reply."
You said "...This is effectively saying that Mary either didn't have free will or that God knew that she would not exercise it. Free will is the essence of original sin."
I respectfully disagree.
God's foreknowledge does not take away from our free will. If I know that my daughter is playing with matches, and I allow her to continue and start the house on fire, I "foreknew" that it would happen. Did I take away her free will? Hardly. Not the best analogy, but it is clear that foreknowledge does not have to interfere with free will.
And your statement regarding "free will is the essence of original sin". You should rethink that - it is ridiculous. God has free will. I suppose He, too, has original sin? And Jesus? And Adam and Eve BEFORE the fall?
God foreknew that Mary would respond "Yes" to the angel. God's plans cannot be overthrown, because of His foreknowledge of events.
Regards
So although the plan of Salvation was ordained before the foundation of the earth God was not sure who the mother would be?