Mary’s own words that God is her Savior.
Only sinners need saviors. If she were sinless, she wouldn’t need a savior, nor would she have been able to receive God’s grace.
Grace only kicks in where sin is.
Also, Mary was worried about Jesus when He was twelve and stayed behind in the Temple.
Worry is a sin.
A savior is one who brings salvation.
To meet God in heaven, one needs to be free of sin.
So one that dies in mortal sin does not gain salvation, and one goes to Purgatory to cleanse oneself of venial sins.
Mary was sinless and was assumed in Heaven.
Since Mary was sinless, why wouldn’t she be able to receive God’s graces? Hail Mary, Full of Grace denotes that Mary has received the great gift of God’s grace. “The Lord is with you.”
You can be a denier or a believer. A mother can worry about her child without it being a sin. Check out Simeon’s Prophecy (Luke2:25-35)and ask why would God tell Mary about the future suffering she will endure?