Pope Shenouda III
The Virgin Is the True Vine
Giving the title 'the true vine' to the Virgin in no way contradicts the title of the Lord Jesus Christ as the True Vine. The Lord is the Vine in one sense and the Virgin is the vine in another.
The Lord is the Vine when we are the branches; He is the Origin and all of us originate from Him; He is the Head and all of us are members of His Body.
As for the Virgin, according to the Church's hymns, she is the one who bore the Fruit of Life - the Son of God. She is the vine who neither experienced senescence nor was reaped by anybody.