Yet not a single verse that says she was without sin - in Greek.
Public revelation ceased with the death of the last Apostle. But these discussions always ignore the fact that the Bible (written revelation) is not the only source available to us from Apostolic times. There's also the preaching (oral teaching) of the Apostles and the lived practice of the Apostles. St. Paul says to pay attention to this.
2 Thessalonians 2:15
traditions which ye have been taught, whether by word, or our epistle.
2 Thessalonians 3:6-9
And we charge you, brethren, in the name of our Lord Jesus Christ, that you withdraw yourselves from every brother walking disorderly, and not according to the tradition which they have received of us.
For yourselves know how you ought to imitate us: for we were not disorderly among you;
Neither did we eat any man's bread for nothing, but in labour and in toil we worked night and day, lest we should be chargeable to any of you.
Not as if we had not power: but that we might give ourselves a pattern unto you, to imitate us.
We are to learn from their words (preaching), their writings (epistles) and their example (we imitate their conduct.)
That's why it seems so unsatisfactory to dismiss some teaching because "Well, that isn't in the Bible." It still part of what the Apostles taught, which is why it is authoritative.
And how do we know it;s what the APostles taught? Becuase it's what was handed on, taught and practiced in all the churches founded by the Aposles. In the churches of northern Africa, Mediterranean Europe, and the Middle East.
All that can be irrelevant, only if the church is irrelevant.
What is the pillar and foundation of the truth?