Excellent job in this debate. Good job of citing specific sources.
One thing I would explain in a different way would be how and when Mary was saved. I think
Stephen Ray illustrates this point well in his video series “Footprints of God” in which he says that there are two ways to “save” someone. One way is to pull them out of the hole after they’ve fallen in. Another is to prevent them from falling in the hole in the first place…I know that Stephen Ray isn’t the only one to make this point in this way, but he is the one that immediately comes to mind.
Second, I would make the point that God DID create other sinless humans…Adam and Eve. They, however, still chose to sin where as Mary did not. Even though God made Adam, Eve, and Mary without sin, he still did give them free will. They still could have chosen to sin.
Also, about the “Full of Grace” vs. “Highly Favored” issue, I will refer you to the CA tract about the Immaculate Conception, although I’m sure you’re familiar with it already:
----"When discussing the Immaculate Conception, an implicit reference can be found in the angel’s greeting to Mary. The angel Gabriel said, “Hail, full of grace, the Lord is with you” (Luke 1:28). The phrase “full of grace” is a translation of the Greek word kecharitomene. This word represents the proper name of the person being addressed by the angel, and it therefore expresses a characteristic quality of Mary.
The traditional translation, “full of grace,” is more accurate than the one found in many recent versions of the New Testament, which give something along the lines of “highly favored daughter.” Mary was indeed a highly favored daughter of God, but the Greek implies more than that (and it never mentions the word for “daughter”). The grace given to Mary is at once permanent and of a unique kind. Kecharitomene is a perfect passive participle of charitoo, meaning “to fill or endow with grace.” Since this term is in the perfect tense, it indicates a perfection of grace that is both intensive and extensive. So, the grace Mary enjoyed was not a result of the angel’s visit, and was only as “full” or strong or complete as possible at any given time, but it extended over the whole of her life, from conception onward. She was in a state of sanctifying grace from the first moment of her existence to have been called “full of grace.”–