"We believe that Mary was a sinner like all humans. She needed a Savior. A wonderful pious woman, yes. But just a woman.
The idea that she never sinned is repugnant for two reasons 1)Christ is the only person who has ever lived without sin. 2)God would have punished a non-sinner with death. Christ's death does not apply here for he became sin for us. The wages of sin is death. If Mary never sinned, then she was made to pay for sins she never committed - for she died."
As I think I have said before, believing that the Theotokos sinned is not some modern Protestant innovation. Sveral of the Fathers, +John Chrysostomos among them, believed that she did. The consensus of the Fathers is, however, otherwise. But that, B, says nothing about her needing a savior. In so saying, you have pointed to what I see as a flaw in the Latin dogma of the Immaculate Conception. If indeed the Theotokos did not live with a nature distorted by the Sin of Adam, the effects of which were absolute bondage to death, then indeed it is a fair question to ask for what reason she needed a savior. Orthodoxy believes that she was graced in such a manner as to avoid all sin in her lifetime, but that was because of her perfect response to God's grace. It has absolutely nothing to do with being born with a different nature than you or me and it is that nature, the one we are born with, which necessitated Christ's death and resurrection, as much for her as for us.
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
Sinlessness is the human nature. Let us recall that sinless Christ is fully human. Immaculate conception in no way denies Mary her humanity. Rather, our sin denies ours.