Nobody said she didn't need a Savior.
Do you believe Mary was sinless? If so, why would she need a Savior?
Whosoever shall not confess that the flesh of the Lord gives life and that it pertains to the Word of God the Father as his very own, but shall pretend that it belongs to another person who is united to him [i.e., the Word] only according to honour, and who has served as a dwelling for the divinity; and shall not rather confess, as we say, that that flesh gives life because it is that of the Word who gives life to all: let him be anathema.
Nestorius: "If any one maintains that the flesh which is united with God the Word is by the power of its own nature life-giving, whereas the Lord himself says, “It is the Spirit that quickens; the flesh profits nothing” John 6:61, let him be anathema. [He adds, “God is a Spirit” John 4:24. If, then, any one maintains that God the Logos has in a carnal manner, in his substance, become flesh, and persists in this with reference to the Lord Christ; who himself after his resurrection said to his disciples, “Handle me and see; for a spirit has not flesh and bones, as you behold me having” Luke 24:39; let him be anathema.]"