Do you believe Mary was sinless? If so, why would she need a Savior?
You can be saved from sin in two ways:
1) By falling into manhole (sin) like all of us and then be saved by being pulled out of the manhole and have yourself cleansed (baptism) - The Lord's work.
2)Or you can be walking along headed right for the manhole (sin) and as you are about to take that final step and descend into it the Lord picks you up and carries you to the other side of it thus saving you. - Also the Lord's work of salvation.