The phrase sets the link between the arrogance and self-sufficiency expressed in Revelation 18:7 (“I sit as a queen…”) and the penalty God details in Revelation 18:8. The Lamb after all is King of kings (and hence of queens), and so the prostitute's boasting must fall flat (Proverbs 11:2; Proverbs 16:18).
8 For this reason her plagues will come in a single day, death and mourning and famine, and she will be burned up with fire; for mighty is the Lord God who has judged her.”