If Mary had refused to bear the Saviour, the Holy Spirit would not have overshadowed her, and she would not have conceived.
God forces Himself on no one.
God "forces Himself" on every one of us who believes in Christ because our rebirth is a supernatural act of God, and not men.
"So then it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy." -- Romans 9:16