Mary admitted that she was a sinner herself by saying that she needed a “savior” in Luke 1:46-47
Nobody had gone to Heaven, not Adam and Eve, nor Moses, Elias, nor Abraham had gone to Heaven until Jesus Christ was born, crucified, died and descended into Hell.
You should thank God that Mary responded positively to the angel Gabriel's Annunciation. (Look it up, it's in the Bible)
We would be all lost, if She had rejected it.