That does not prove The Blessed Virgin Mary was a sinner. It proves that all people without salvation are unrighteous, that is, not even one is righteous.
Oh, this is good. So, you think you are righteous as a believer?
Then you quoted this:
"But go and learn what this means: ‘I desire mercy, not sacrifice.' For I have not come to call the righteous, but sinners.(Mat 9:13)"
Yes, go learn what that means. I'll help you: Jesus didn't come to call those who think that they are righteous (like yourself), but sinners.
There are two types of sinners:
1] The self-righteous...like your Pope
2] Those who know they are sinners and need Christ's righteousness.
What Jesus is saying is He didn't come to save the self-righteous because it is very hard to convince a holy Joe that he is a sinner.
Try again,
RobertH.