Okay, I think what we have here is a combination of poor formatting and punctuation and careless reading. I’m going to format that section as though it were a regular book.
To become the mother of the Savior, Mary “was enriched by God with gifts appropriate to such a role.” The angel Gabriel at the moment of the annunciation salutes her as “full of grace”. In fact, in order for Mary to be able to give the free assent of her faith to the announcement of her vocation, it was necessary that she be wholly borne by God’s grace.
Through the centuries the Church has become ever more aware that Mary, “full of grace” through God, was redeemed from the moment of her conception. That is what the dogma of the Immaculate Conception confesses, as Pope Pius IX proclaimed in 1854:
The most Blessed Virgin Mary was, from the first moment of her conception, by a singular grace and privilege of almighty God and by virtue of the merits of Jesus Christ, Savior of the human race, preserved immune from all stain of original sin.
The “splendor of an entirely unique holiness” by which Mary is “enriched from the first instant of her conception” comes wholly from Christ: she is “redeemed, in a more exalted fashion, by reason of the merits of her Son”. The Father blessed Mary more than any other created person “in Christ with every spiritual blessing in the heavenly places” and chose her “in Christ before the foundation of the world, to be holy and blameless before him in love”.
The Fathers of the Eastern tradition call the Mother of God “the All-Holy” (Panagia), and celebrate her as “free from any stain of sin, as though fashioned by the Holy Spirit and formed as a new creature”. By the grace of God Mary remained free of every personal sin her whole life long.
“Let it be done to me according to your word. . .”
At the announcement that she would give birth to “the Son of the Most High” without knowing man, by the power of the Holy Spirit, Mary responded with the obedience of faith, certain that “with God nothing will be impossible”: “Behold, I am the handmaid of the Lord; let it be [done] to me according to your word.” Thus, giving her consent to God’s word, Mary becomes the mother of Jesus. Espousing the divine will for salvation wholeheartedly, without a single sin to restrain her, she gave herself entirely to the person and to the work of her Son; she did so in order to serve the mystery of redemption with him and dependent on him, by God’s grace:
As St. Irenaeus says, “Being obedient she became the cause of salvation for herself and for the whole human race.” Hence not a few of the early Fathers gladly assert. . .: “The knot of Eve’s disobedience was untied by Mary’s obedience: what the virgin Eve bound through her disbelief, Mary loosened by her faith.” Comparing her with Eve, they call Mary “the Mother of the living” and frequently claim: “Death through Eve, life through Mary.”
Mary’s divine motherhood
Called in the Gospels “the mother of Jesus”, Mary is acclaimed by Elizabeth, at the prompting of the Spirit and even before the birth of her son, as “the mother of my Lord”. In fact, the One whom she conceived as man by the Holy Spirit, who truly became her Son according to the flesh, was none other than the Father’s eternal Son, the second person of the Holy Trinity. Hence the Church confesses that Mary is truly “Mother of God” (Theotokos).
Read this way, I think it is clear that the paragraph’s leading reference to the Fathers of the Eastern tradition pertains also to the final sentence, “By the grace of God Mary remained free of every personal sin her whole life long.” That is, it is correctly read, “For the Fathers of the Eastern tradition, Mary remained free of every personal sin her whole life long by the grace of God.”
Of course, if you find other references in the Catechism or other official documents which show that I am in error, I’ll have to reconsider.
You stated "Catholic doctrine does not claim that Mary never committed a single sin, no matter how slight," in other words the Church doctrine teaches that Mary may have sinned.
My point is that the Church doctrine claims that Mary never sinned.
It has nothing to do with formatting. Your statement is simply not what the Catholic Church teaches, period.