Did the Blessed Mother have a sister?
Possibly. Scripture states:
But standing by the cross of Jesus were his mother, and his mother’s sister, Mary the wife of Clopas, and Mary Magdalene (John 19:25).
Since it is unlikely that two daughters of the same parents would have the same first name of Mary, it is more likely that the wife of Clopas was a more distantly-related kinswoman.