"Who can measure the sorrows of Our Lady? The fullness of grace abiding in her, infused her with a love that completely transcended our human limitations. Because of this, her sorrow likewise knew no bounds. The two realities in her have been linked at various times to other titles, most notably "Our Lady of Compassion" and "Our Lady of Hope," both beautiful because they speak to this union of love and sorrow. Simeon’s prophecy, as Mary and Joseph present the infant Jesus in the Temple, is the first public pronouncement to Mary of where her relationship with the God-Man, her child, will take her (Luke 2:34-35)."
The Reformation Study Bible has this footnote: "2:35 sword. The sword imagery means that all this will not be without cost to Mary as she sees her Son rejected and crucified. The sword does not refer to any atoning work, but of the deep anguish it will cost her."
The Roman Catholic New American Bible Revised Edition has this footnote on Luke 2:35: "[2:35] (And you yourself a sword will pierce): Mary herself will not be untouched by the various reactions to the role of Jesus (Lk 2:34). Her blessedness as mother of the Lord will be challenged by her son who describes true blessedness as “hearing the word of God and observing it” (Lk 11:27–28 and Lk 8:20–21)."
As the above two cited commentaries make evident, there is nothing in Luke 2:34-35 about Mary participating in the atonement of Jesus Christ. That is a foreign concept which has to be read into the text of Scripture.
There is nothing in this passage about Mary "taking on a universal motherhood for all of us." Such a presupposition is driven by a wild desire to turn Mary into some sort of a goddess.