Adam and Eve were created without sin but did not remain sinless and entered into a fallen state that was passed on to all their descendants. Simply because, at her conception, God blessed and protected Mary from this fallen state/Original Sin, so that his son would enter into the world without sin touching him, either. Mary immediately noted God as her savior; not that she was justified before God by her own efforts. God created each one of us for a purpose, and God provides each one of us all we need to fulfill that purpose. Jesus was fully human, and growing up, the example of a sinless mother would have been additional protection for a young child. Again, who provided this sinless state? God--to provide Mary all she needed to fulfill her purpose before Him. Mary should be seen through Jesus, not Jesus seen through Mary.