St. Louis de Montfort was a Catholic... in fact, a Catholic 'saint'.
As a Catholic and as a 'saint' he believed that:
“The saints have said many beautiful things about Mary… They knew that there were no limits to her power, because she has power over God Himself.” (p. 3)
“When the saints tells us that all things in heaven and on earth, including God Himself, are subjected to the Blessed Virgin, they mean that the authority God gave her is so great that she appears to have the same power as the Trinity, and that her prayers and requests have such an effect upon God that He receives them as commands.” (p. 9)
“Mary, being altogether transformed into God by grace and by the glory which transforms all the saints into Him, … that in heaven and on earth everything, even God Himself, is subject to the Blessed Virgin, …” (p. 17)
“Moreover, if, as I have said, the holy Virgin is the Queen and Sovereign of heaven and earth, has she not then as many subjects and slaves as there are creatures? … ‘behold, all things, and God included, are subject to the empire of the Virgin’.” (p. 55)
-Saint Louis Grignion DeMonfort,
True Devotion To Mary
This book should have been condemned by the Catholic Church if they do not conform with what De Montfort has proclaimed.
“St. Bernardine of Siena declares that all obey Mary’s commands, even God"
-J. Alberione]
Glories and Virtues of Mary
p. 177
If Catholics do not believe that Mary is powerful than God, De Montfort, Bernardine, and other saints mentioned in the book should have not been canonized by the Church authorities.