For Christians, the word of God (the Bible) tells us what to believe and do; but, for R.C.s, it's their "Magisterium" that tells them what they must believe and do. This is why that R.C. site kept mentioning the "Magisterium".
The site refers to many pronouncements by the R.C. "Magisterium".
Here's a longish quote from the site to which I linked (it quotes official R.C. sources).
"Leo XIII offers a dynamic portrayal of Mary's coredemptive suffering: She painfully partakes in "
His torments in the very depths of her soul," "
weeping" at the cross of her dying Son and willingly
offers him to divine justice. This coredemptive suffering with the Redeemer was fitting and appropriate so that Mary "
might receive us as her children."
Thus beyond endorsing the Marian roles of Mediatrix, Reparatrix and Conciliatrix, Leo XIII brings to light the precious gift generously given to Mary by divine will: her cooperation in the acquisition of the graces of redemption. She has been granted "
an almost boundless power" in dispensing the very graces won by her coredemptive participation with the Redeemer:
The Pope's depiction of Mary's vocation is so astonishing that we might not fully appreciate its importance. Mary's ancient title
Domina is usually translated into English by the very weak "
our lady." However, that word's counterpart is
Dominus - LORD! In Sacred Scripture, "
Lord" is unambiguous for God Himself, even more clearly than "
Son of God." Yet
Domina is one of Mary's titles that the Pope uses in the context of our Redemption by Christ. Also, the significance of
Adiutricem populi is further heightened when Vatican II, calling Mary "
Advocate, Auxiliatrix, Adjutrix, and Mediatrix," refers us back to this encyclical.
[15]
"
We have shown that the Rosary,...coupled with [Mary's] office of mediatrix [mediationis officio], is a most excellent and fruitful prayer of petition."
[16] Pope Leo XIII draws the Christian faithful to recall the truths of the Rosary, prayer and our Lady's mediating role which include her effective and unique participation in Redemption:
This remarkable concatenation of Mary's prerogatives depicts her cooperation with her Son. It is cooperation that is 1) direct, immediate and dynamic; 2) bilateral, between Mary and Jesus precisely in His role as Redeemer; 3) not only an activity but a ministry - a role initiated by Him and assigned to her by Him to achieve our Redemption. In these succinct quotations of Pope Leo XIII we see the Magisterium's fullest description to date of the essence of Mary's role as Coredemptrix.
15.
Documents of Vatican II,
LG no. 62, pg. 91, n. 278.
16.
Diuturni temporis spatium, September 5, 1898,
ASS 31(1898-1899) 147.
17.
Parta humano generi, September 8, 1901,
ASS 34 (1901-1902): 194-195."
It is not only in catechisms that we find the official teachings of the R.C. "Magisterium", so you cannot demand that quotes be limited to those.