I think you base this assumption on a faulty perception of what "participation" is. No one participated more fully in the Holy Sacrifice than Our Blessed Mother, and "all" she did was remain silent at the foot of the cross.
Very well put...
Perhaps. The Scripture doesn't detail what exactly she was doing. However, one presumes that she was striken with sorrow. Knowing what she was told regarding her Son and on what she pondered upon, it is likely that she was actively offering her own motherly ties up to the Father as a sacrifice in her own sense. Most mothers would desire to hold on to her son in such a situation. The Church teaches that Mary was abandoning this concept as an incredible spiritual sacrifice on her part.
This is quite different from a person who is present ONLY in body to what is happening in another language 50 yards away. In many cases, I think people were there merely to fulfill their "duty" to appear at Sunday Mass, rather than "participating" in that one-time offering of Christ on the Cross... That is the impression I get from when I was a youngster. The reading of other books or reciting the rosary during the Mass is pretty good evidence that a person's mind was elsewhere. Recall the Scriptures teach that our inner dispositions are much more important than our outer activities. Being in the building of the Church while the Mass is proceeding is not the same thing as participating in the sacrifice of Christ on the Cross.
Regards