Would God have chosen someone unsuitable to be the mother of His Son? We know that Jesus revered His Mother, and Jesus, being the Second Person of the Trinity is part of God, so I'd assume that yes, God revered Mary as well. That doesn't mean that Mary is equal with God, but it does mean that we should revere her, above all other human beings, except for Jesus.
God chooses whom He wills. It may not seem "logical" but there you go. God knows better than us.
Some would have considered, for example, that David was unsuitable to carry the line of Christ since he was guilty of adultery and murder. Yet God chose him. David praised God for bestowing grace on him despite his sin; Mary did the same.