I would have to posit that God could indeed have rendered Mary pure and sinless - He did it for David in the OT and then He did it again for all of us who have given ourselves to Christ since. Sin is sin and pure is pure. Praise God! I am saved and pure in His sight!
God can do whatever he wants. He’s not going to be constrained by anything we say or do or read. God will have the last word. Guaranteed.