Hi Fox!
Mary is a human being and therefore dependent on God’s action in Jesus. Not simply Mary as a person, but Mary as a member of humankind depended upon Him. Human nature itself was fallen. It makes no difference what the time sequence was. Chronologically Abraham and Isaac predated Jesus but they no less depend for their salvation on Jesus.
An innocent baby might die sinless as may a mentally handicapped person, but their eternal happiness, their salvation if you wish, their belonging to redeemed human nature, is owed to Jesus. If Mary chose not to sin, that doesn’t make her less human nor less a recipient of the joy of heaven due to God’s incarnation and redemption in Jesus