Sorry; but there was nothing to 'decline'.
GOD said THIS is what's going to happen; and it did.
Well, that is true. In general God knows out intentions and our actions before we know them and act on them. This does not mean we are not free to act at the time that we decide to act.
“Secondly, she could have lawfully declined at the Annunciation as any woman may.
Sorry; but there was nothing to ‘decline’.
GOD said THIS is what’s going to happen; and it did.”
Yes, I don’t recall Gabriel asking Mary if she wanted to do this...it was told to Mary that this would happen.