Nowhere is Scripture does it tell us that Mary was sinless. She was as much in need of a Saviour as Adam and Eve after the Fall.
She needed a Savior because He saved her from the effects of Original Sin.
Why do I think that? Because in the Bible, when God addresses you by a new name, it's always very significant. It tells you what you really are: what you are in God's eyes.
There's all kinds of discussion about what Kecharitomene means (Link), but a lexical analysis of the word indicates 'being made fully acceptable,' 'being given the highest favor,' 'being made the most blessed among women' --- which is what the Angel Gabriel in fact explains her right after he addresses her as "Kecharitomene."
That cannot possibly mean she is no better than a damaged daughter of disobedient Eve. It means she has been given the highest favor. That would make her equal to Eve, not after the Fall, but at the height of Eve's blessedness before the Fall.
You may not agree with that, but it is the unprecedented fact about Mary which was acknowldged by the Angelic Salutation.
It was completely and entirely the grace of God: unmerited favor.
Of course she needed a Savior. It is the Savior's action and merit, and his alone, which did this great thing for her.
You think she was a sinner. But I see no reason to believe you, rather than the angel.