Which is her admission that she HAD sinned. If she was born without the stain of original sin, and led a perfect sinless life, then she would not have needed a savior.
If that were the case, then when she called God her *savior* she would have been lying, which would have been a sin.
So then she wasn't sinless.
Can God save us?
Yes?
Can He save us at anytime of His choosing?
Yes, He is sovereign.
Did God save Mary at the time of His choosing?
Yes.
Was that saving dependent on the merits of Jesus Christ?
Yes?
How can that be if Jesus was not yet Incarnate and certainly had not died on the Cross and had not yet been resurrected?
Because Jesus being God is also eternal and His merits do not have to be limited to our understanding of time. He could apply those merits to His mother even before His incarnation.