“For all have sinned and fall short of the glory of God” only holds true for the context it’s written. Both Jews and Gentiles need redemption. It has no context to individual people.
Just as when Paul writes two chapters later -- ”so death spread to all men because all men sin” – the context is that both Jews and Gentiles have experienced death because of sin. We know that “all” here isn’t referring to all individuals because all did not experience death. To try to make the context of the first “all” be different than the second “all” in the short phrase ”so death spread to all men because all men sin” would be poor scholarship indeed.
I’m not sola-Scriptura; I don’t need an explicit statement that Mary did not sin. You should require one for yourself that she did sin however before professing that as truth.
I do believe the fact that she was sinless is reflected in Scripture. For one thing, when she is addressed by the angel Gabriel, he refers to her as “full of grace.” He doesn’t use it as an adjective to describe her; he uses it as her name, a title. The Greek word used in that passage is “Kecharitomene.” My understanding is that is in the perfect tense of the word, which would indicate both a past and present form. Regardless of whether you accept that, it is a unique form of the word of the Greek root word for grace charis, and is used exclusively in Scripture for Mary.
I think Mary herself tells us she is sinless when she professes that “My soul magnifies the Lord and my spirit rejoices in God my savior” Luke 1:46-47). To magnify means to enlarge or bring into focus. I have searched the Scriptures for another instance when a person’s soul is referred to in this way and I have never found anything even remotely close. A soul marred by sin would not “magnify” the Lord; a perfectly sanctified soul would.
Aside from those clues about the state of Mary’s soul, I have no doubt that as a culture we have absolutely lost the sense of the sacred known to the Jewish people. Moses removed his sandals when he approached the holy ground of the burning bush. There are pages and pages of Scripture devoted to the construction of the tent of the meeting and the ark of the covenant and how they were perfectly sanctified before God came to dwell there among His people. To understand it is perfectly fitting for the woman that the King of Kings would take flesh from and dwell within would be perfectly sanctified from sin is consistent with how Scripture teaches us over and over again that God is Holy.