I use the word “dormition” (sleep) in the title as Our Lord used it in referring to the death of Lazarus. Our Lady did truly die, desiring to be in all things like Jesus, as the article that follows demonstrates from tradition. Mary was in the tomb for forty hours, just as was her Son. She did not rise from the dead but was assumed, body and soul, into heaven by the power of God, whereas Jesus rose by His divine power.
The Remnant, Robert J. Siscoe: On December 8, 1854, in the Constitution Ineffabilis Deus, Bl. Pope Pius IX defined the dogma of the Immaculate Conception of the Blessed Virgin Mary. Many non-Catholics mistakenly believe the Immaculate Conception refers to the virginal conception of Jesus Christ in the womb of His mother. In reality, the term refers to the conception of the Virgin Mary in the womb of her mother, St. Anne. Through the merits of Jesus Christ, the Blessed Virgin Mary received the singular privilege of being exempt from the universal law of sin from the moment of her conception. The dogmatic definition reads as follows: “the most Blessed Virgin Mary … in the first instance of her conception, by a singular privilege and grace granted by God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved exempt from all stain of original sin”. Full article is here.