suffer horribly and die for us made Him unbelievably special. But no one can deny that Mary's fiat played a big role in salvation history.
As far as being a sinner, remember when the angel Gabriel came to her asking for that critical fiat to become the mother of the Savior?
Keep in mind that the angel Gabriel used the word "Hail" was used for someone of a much higher ranking than oneself, such as a commoner to a king.
https://www.catholic.com/magazine/print-edition/hail-mary-conceived-without-sin
Gabriel greeted Mary: "And [the angel Gabriel] came to [Mary] and said, “Hail, full of grace, the Lord is with you!” But she was greatly troubled at the saying, and considered in her mind what sort of greeting this might be. And the angel said to her, “Do not be afraid, Mary, for you have found favor with God” (Luke 1:28-30).
...The angel actually communicated a new name or title to her... In Greek, the greeting was kaire, kekaritomene, or “hail, full of grace.” Generally speaking, when one greeted another with kaire, a name or title would be found in the immediate context. “Hail, king of the Jews” in John 19:3 and “Claudias Lysias, to his Excellency the governor Felix, greeting” (Acts 23:26) are two biblical examples of this.
The fact that the angel replaces Mary’s name in the greeting with “full of grace” was anything but common...
In Hebrew culture, names and name changes tell us something permanent about the character and calling of the one named. Just recall the name changes of Abram to Abraham (from “father” to “father of the multitudes”) in Genesis 17:5, Saray to Sarah (“my princess” to “princess”) in Genesis 17:15, and Jacob to Israel (“supplanter” to “he who prevails with God”) in Genesis 32:28.
In each case, the names reveal something permanent about the one named. Abraham and Sarah transition from being a “father” and “princess” of one family to being “father” and “princess” or “mother” of the entire people of God (see Rom. 4:1-18; Isa. 51:1-2). They become patriarch and matriarch of God’s people forever. Jacob/Israel becomes the patriarch whose name, “he who prevails with God,” continues forever in the Church, which is called “the Israel of God” (Gal. 6:16). The people of God will forever “prevail with God” in the image of the patriarch Jacob.
What’s in a name? According to Scripture, quite a lot.
St. Luke uses the perfect passive participle, kekaritomene, as his “name” for Mary. This word literally means “she who has been graced” in a completed sense. This verbal adjective, “graced,” is not just describing a simple past action. Greek has another tense for that. The perfect tense is used to indicate that an action has been completed in the past, resulting in a present state of being. “Full of grace” is Mary’s name. So what does it tell us about Mary? Well, the average Christian is not completed in grace and in a permanent sense (see Phil. 3:8-12). But according to the angel, Mary is. You and I sin, not because of grace, but because of a lack of grace, or a lack of our cooperation with grace, in our lives. This greeting of the angel is one clue into the unique character and calling of the Mother of God. Only Mary is given the name “full of grace,” and in the perfect tense, indicating that this permanent state of Mary was completed...
and of course, as mentioned earlier in this thread, the Early Church Fathers taught that Mary was sinless:
https://www.catholic.com/tract/mary-full-of-grace