I think you are misunderstanding this. God cannot be in an impure vessel without consuming it. Even Mary attributes her sinlessness to Her Son ...her Savior.
Look at all the early writings of the Fathers of the Church. They all believed the same thing. Even Martin Luther believed it. There is nothing about this belief that denies that Jesus paid the price for our sins on the cross. This is one of the reasons that we Catholics place Christ on the Cross in our church buildings....so that we NEVER forget what the cost was of our salvation.
Oh hogwash...God can and does anything he wants with whomever he wants, he is not bound by any thing of man....either he's sovereign or he's not.
There is nowhere where Mary attributes her sinless "vessel" to her Son except in catholic teachings and how they distort the scriptures to justify their doctrines.
Jesus isn't on the cross anymore...He arose...Catholics would do well to amplify this by showing the cross without him 'still' struggling there....
He said...It's finished". .....Mary is NOT Co-Redemptrix with Jesus. She was not on the cross nor did she arise... Mary does Not sanctify souls, nor is she anyone's 'spiritual mother', and further.... she does not dispense grace.
We do NOT consecrate ourselves to a sinner named Mary whom God used as a biological vessel. We give ourselves wholly and totally to Jesus, the 'only' worthy one in the universe.