The "Immaculate Conception" was made up out of whole cloth.
Wasn't "The Immaculate Conception" the conception of Jesus? To my knowledge only Jesus and Adam were created without the introduction of male and female sex cells (sperm and ovum).
I thought the "Immaculate" part of Jesus' Immaculate Conception was the fact that Mary "had not known man."
As far as Mary being "full of Grace," any forgiven sinner can tell describe the sensation of being "full of Grace."