The most Blessed Virgin Mary was, from the first moments of her conception, by a singular grace and privilege of almighty God and by virtue of the merits of Jesus Christ, Savior of the Human race, preserved immune from all stain of Original Sin.
How do you get from that to your statement?
If she was sinless, she didn’t need a savior. Only sinners need a savior.
By her calling God her savior, it was her tacit admission of her sinfulness.