I have heard many Protestants claim that all of their sins past, present and future were washed away by the Blood of Jesus. It is an indication of a belief in a limited God to believe that He could not do so to preserve Mary from sin from the moment of Her conception.
Peace be with you
Well, the Protestants could very well be correct, and it is enlightening to see that you apparently agree.
As for Mary, of course He could have.
And I'm sure if He did, He also would have considered it important enough to put into the Holy Scriptures.
It can't be found there.
Neither can her "assumption" which is "assumed" by some.
God knew what he was doing, and had COMPLETE control over the situation. After all, she was conceived by the Holy Spirit.