Mary, a young girl, a regular human being, same as the rest of us, had a pure heart, God chose her to bear the Lord Jesus: God chose a regular human being to do this, one who was EXACTLY the same as everyone else. Yes, she had a pure heart, praise God, she was a sweet young girl whose heart was pure. That does not make her anything else, she was simply a normal human being with a pure heart. That’s how Jesus was able to be wholly human. Because His mom was wholly human.
This is plainly obvious with a very basic reading of Scripture. Plain. Obvious. Open the Bible and read it. It’s there, plain as day.