As Father René Laurentin states, "Mary is part of the three phases of the history of salvation: the time which precedes Christ, the years of his earthly life, and the era after Christ."
She is there when the Church is born
Daughter of Zion become Mother of the Messiah and Redeemer of Man, Mary is there when the Church takes her first steps around the Twelve apostles in Jerusalem, where she witnessed with them the events of the Passion of her Son, of His Resurrection, of His Ascension, finally that of the First Pentecost. The Twelve and the first disciples began to meet in the Upper Room at first, later they would go to one or the other's house in Jerusalem, and Mary prayed with them and sustained their faith, hope and charity, like a mother encourages her children.
She is there in the course of temporal human history
Mother of God and now universal Mother, mother given to the world by "her Son on Calvary ("Behold your son", Jn 19: 26), Mary is at the same time the one who intercedes, who become a mediatrix for her children, at each stage of the life of the Church and all around the world... Sometimes Mary even intervenes directly in human history to transform its outcome (one example would be the victorious battle of Vienna in 1683), also to warn her children of an imminent danger, or to deliver a message to the entire world (cf the apparitions Lourdes and Fatima...).
She is present more and more as a constant model for the Church, to whom she gives birth, until the Parousia
Mary raises her children and never ceases to give birth to them in a spiritual way, until the Last Advent when the mystical Body - the Church - will have reached its maturity. She is a model of faith, hope and charity for all humanity.
"Since she is the dawn which precedes and finally reveals the Sun of justice - i.e. Jesus Christ - she must be known and recognized so Jesus Christ can be too," once said Saint Louis de Montfort, stating that the closer we get to the end times, the more visible Mary's presence in the Church becomes. This is how the multiplication of Marian apparitions in the last two centuries can be explained...