Mary in the Economy of Salvation

After this manner the Blessed Virgin advanced in her pilgrimage of faith, and faithfully persevered in her union with her Son unto the cross, where she stood, in keeping with the divine plan, grieving exceedingly with her only begotten Son, uniting herself with a maternal heart with His sacrifice, and lovingly consenting to the immolation of this Victim which she herself had brought forth.

Lumen Gentium, chapter II, n°58