Recent scientific studies could shed light on one of the ways in which Mary was unique.
When a child grows in his or her mother’s womb, the mother and child have a special symbiotic relationship. As this article (among many others) shows, some stem cells from the fetus transfer to the mother’s body, and often stay there for years (and possibly vice versa). As this same article reveals, it seems that these stem cells might not be just hanging around; they may take an active role in healing certain kinds of injuries (and, in some cases, causing certain problems).
Think about that for a moment. If this science is correct, then Mary was probably carrying around living cells from Jesus’ body inside her own. Catholics believe that Jesus’ body is inextricably joined to his divinity (just think of the Eucharist). So, if all of this is true, then Mary’s body was, in a certain real and physical sense, permeated by God’s presence, in a way far more intimate even than when people receive Communion. Think of the effects the Church attributes to receiving Communion, and intensify that immeasurably.
Suddenly the doctrine of the bodily Assumption of Mary into heaven at the end of her earthly life makes more sense than ever. Not to mention her remaining free from sin.