Considering the lack of detail about Mary in Scripture, one can not point to times when she sinned. However, I find some of her behavior interesting in Scripture. First, when Jesus was Left behind in Jerusalem and she sorta rebukes Jesus "Son, why hast thou thus dealt with us? behold, thy father and I have sought thee sorrowing."
Luke 2:33 speaks of Simeon's blessing and then adds "And Joseph and his mother marvelled at those things which were spoken of him."
Jesus's comment in Luke 8:21
And he answered and said unto them, My mother and my brethren are these which hear the word of God, and do it. (like Mary and his brothers weren't hearing and doing the word of God at the time - they weren't yet believers).
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Jesus's (perhaps gentle) rebuke of Mary in John: 4Jesus saith unto her, Woman, what have I to do with thee? mine hour is not yet come.
Sometimes it seems as if Mary wasn't fully aware of who Jesus was (certainly not His Godhood). She was aware her child was special. But, I don't think she "got" the full implications. I also don't think that she or his brothers were fully converted until after His resurrection. They travelled with him at Cana into Capernaum but later they don't seem to be with him and his disciples as they travelled. You do see them in the upper room later clearly as believers
"Jesus's (perhaps gentle) rebuke of Mary in John: 4Jesus saith unto her, Woman, what have I to do with thee? mine hour is not yet come."
That's the line +John Chrysostomos pointed to. Like I have said, your position is not unknown among the Fathers. But he also penned this:
"Through the prayers of the Theotokos, Savior, save us!"
and
"It is truly meet to bless thee, O Theotokos, who art ever blessed and all-blameless, and the mother of our God. More honorable than the Cherubim, and more glorious beyond compare than the Seraphim, thou who without stain barest God the Word, and art truly Theotokos: we magnify thee."
among other prayers.