Mary DID have a choice. She had free will. I know that’s hard for you Calvinists to accept, but she could have said NO! The angel Gabriel didn’t say, “Mary, you’re already pregnant!” Reread the story again, and ponder it until you get what a singular act it is. Mary’s YES is 180 degrees opposite of Eve’s NO.
The angel Gabriel DID say, “Mary, you’re gonna be pregnant!”
Mary would have looked a bit more stupid than Rome's caricature if she'd said, "No; I ain't!"