Mary was amazingly blessed by God to bear Messiah.
Scripture never says she is blessed to a place above other woman, but "blessed among women."
Of all women, she alone was selected to bear Messiah.
She isn't above anyone else. Scripture doesn't say this.
As to "calling her Blessed," literally the Greek says...
"For He has had regard for the humble state of His bondslave;
For behold, from this time on all generations will count me blessed."
It doesn't say everyone is to call her "Blessed Mary."
11We count blessed those who endured. You have heard of the endurance of Job and have seen the outcome of the Lord’s dealings, that the Lord is full of compassion and is merciful. (NASB)
It's use is not unique to Mary.
The verb, μακαρίζω (makarizó) conveys the meaning of: pronounce blessed, as the result of enjoying the benefits (privileges) that (literally) extend from God. See 3107 (makarios).http://biblehub.com/greek/3106.htm
We like to fulfill this prophecy with joy, because Scripture says she's our mother: precisely in that section about the Mother of the Messiah, the "Woman Clothed with the Sun" which says we are "the rest of her offspring":
Revelation 12:17
Then the dragon was enraged at the woman and went off to wage war against the rest of her offspring --- those who keep God’s commands and hold fast their testimony about Jesus.
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Luke 7:28 I tell you, among those born of women none is greater than John. Yet the one who is least in the kingdom of God is greater than he.”