The Prayer of the Faithful is to be concluded by the Priest as presider, in the person of Christ, addressing an oration, or formal prayer, to God. Since the prayer is in a sense, Christ addressing God, replacing the oration with a communal recitation of a prayer to Mary or any Saint misses the point of this part of the Mass. Our Lady would want us to be humble and obedient. 
 
GIRM 71 says,"It is for the Priest Celebrant to regulate this prayer [of the Faithful] from the chair. He himself begins it with a brief introduction, by which he calls upon the faithful to pray, and likewise he concludes it with an oration." ​An oration is a formal, liturgical prayer offered by the Priest Celebrant. (See Fr. John Hardon's definition of "oration" at Catholic Culture.) 
 
GIRM 30 states: "Among those things assigned to the Priest, the prime place is occupied by the Eucharistic Prayer, which is the high point of the whole celebration. Next are the orations, that is to say, the Collect, the Prayer over the Offerings, and the Prayer after Communion. These prayers are addressed to God by the Priest who presides over the assembly in the person of Christ, in the name of the entire holy people and of all present. Hence they are rightly called the “presidential prayers.""
 
GIRM 32 states: "The nature of the “presidential” parts requires that they be spoken in a loud and clear voice and that everyone listen to them attentively. Therefore, while the Priest is pronouncing them, there should be no other prayers or singing, and the organ or other musical instruments should be silent."