John 6:40 disagrees with you as does John 3:16....and the rest of the New Testament.
No mention of Mary needing to be sinless for salvation....only belief in Christ.
John 6:38 is the verse you should be looking at.
Why is it Jesus’s will to do the will of the Father?
What will are we talking about?
Where does it come from?
If Jesus has a fully human nature, where did he get it?
If Mary had a fallen human nature, how could she give complete assent to the Incarnation?
If Mary did not give complete assent to the Incarnation, is God a rapist?
If Mary did not give complete assent to the Incarnation, is Jesus really one of us?
If Jesus received a tainted human nature from his mother, how could he be wholly conformed to the will of his Father?
There is no atonement without the Immaculate Conception.