Munificentissimus Deus §40 (Mary as Queen; compare Lumen Gentium §59 and CCC 966) — Vatican.va English translation of Munificentissimus Deus (1 November 1950) (official text, quoted at the cited paragraph)
40. Hence the revered Mother of God, from all eternity joined in a hidden way with Jesus Christ in one and the same decree of predestination, immaculate in her conception, a most perfect virgin in her divine motherhood, the noble associate of the divine Redeemer who has won a complete triumph over sin and its consequences, finally obtained, as the supreme culmination of her privileges, that she should be preserved free from the corruption of the tomb and that, like her own Son, having overcome death, she might be taken up body and soul to the glory of heaven where, as Queen, she sits in splendor at the right hand of her Son, the immortal King of the Ages.
This text is under copyright; the cited paragraph is quoted for study, with a link to the full document. Translation: Vatican.va English translation of Munificentissimus Deus (1 November 1950).
Why Pitre cites it
Pius XII on Mary's queenship: 'as Queen, she sits in splendor at the right hand of her Son.' The sentence Pitre quotes through the Catechism — 'exalted by the Lord as Queen over all things, so that she might be the more fully conformed to her Son' (CCC 966) — is Lumen Gentium 59, which builds on this constitution's definition of the Assumption.
Notes
The phrase "exalted by the Lord as Queen over all things" is NOT in Munificentissimus Deus. CCC 966 is quoting Lumen Gentium 59 (which itself cites MD, DS 3903). Vatican.va's LG 59 reads: "Finally, the Immaculate Virgin, preserved free from all guilt of original sin, on the completion of her earthly sojourn, was taken up body and soul into heavenly glory, and exalted by the Lord as Queen of the universe, that she might be the more fully conformed to her Son, the Lord of lords and the conqueror of sin and death." The nearest MD passage is §40 (given here), where Mary is "taken up body and soul to the glory of heaven where, as Queen, she sits in splendor at the right hand of her Son, the immortal King of the Ages." The definition itself is §44. Footnote numbers (47)–(48) removed.