If Mary was born sinless, she didn't need a savior. If she was sinless and called God her savior, then she lied.
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Unless she was born sinless because of her son Jesus Christ. Since God exists in eternity beyond time there is nothing preventing him applying the merits of our Lord's sacrifice on the Cross to Mary at her conception.
Mary was sinless because God preserved her from sin. It wasn’t by her own power that she was conceived without original sin. Therefore she has a savior.