If Mary were without sin.. why would she know that she needs a savior?
The Church has a simple and sensible answer to this difficulty. It is this: Mary, too, required a Savior. Like all other descendants of Adam, by her nature she was subject to the necessity of contracting Original Sin. But by a special intervention of God, undertaken at the instant she was conceived, she was preserved from the stain of Original Sin and certain of its consequences. She was therefore redeemed by the grace of Christ, but in a special way, by anticipation. The doctrine of the Immaculate Conception thus does not contradict Luke 1:47.God bless.