God is no trickster. He doesn't try to fool us into doing His will. He wants our full assent knowing how difficult conforming our will to His may be. So how much did Gabriel reveal to Mary about the suffering she would share with her Son? Fulton Sheen believed that Mary knew the depth of pain and grief she was choosing. Here's how he describes it:
Mary’s participation in Christ’s suffering began with the annunciation, when she was asked to give God a human body, more properly, a human nature. In other words, will you make God capable of suffering? God though he was, he learned obedience in the school of suffering. God could know experimentally what suffering was only by taking a body. So the Blessed Mother is asked, ‘Will you make it possible for your creator to suffer?’ Think of a mother, for example, who gives to a young son or daughter an automobile at the age of nineteen, which a short time afterwards is the cause of a wreck and permanent injury. Would the mother ever forgive herself? And here Mary has to say yes, I will let him suffer.If you think about it, Mary knowing makes absolute sense. Preserved from original sin, she had an unfallen intellect. She had to be the most intelligent, wisest, and most insightful human creature to ever live. She studied the scriptures. She knew what the prophets taught about the Messiah. She could have instructed the disciples on the road to Emmaus so well versed was she in the truths of God.
Think of the icon of Our Lady of Perpetual Help with the two angels bearing the instruments of torture. Even if she wasn't fully aware at the Incarnation, she was being prepared just as Jesus was by continuous intimate union with God in His Three Persons.
We all know mothers who suffer -- some from the loss of a beloved child, others from the pain of spiritual loss when children reject them and their values. If God sent an angel asking you to agree to gruesome torture and death for one of your children, how would you respond? Could you, would you say, "Yes. Thy will, not my will, be done."? As a mother and grandmother I pray every day that I will not have the pain of seeing one of my children or grandchildren suffer and die before I do. I pray that, if the Lord ever burdens me with such a suffering, I will say yes.
Our Lady of Sorrows, pray for us.