That question is trickier than it sounds because it depends on what you define as the 'queen's realm.' If we're talking about a kingdom where a queen is the central authority and the plot is confined to her castle or court, then Sarah J. Maas's 'A Court of Thorns and Roses' series comes to mind, especially the later books. While they travel between courts, a huge chunk of the political machinations and personal drama happens within the confines of the Night Court's palace under High Lady Feyre's rule. It's less about conquering new lands and more about managing the realm she has. The domestic scenes in the River House or the political strategy sessions in the library feel deeply rooted in that one space.
Another classic is 'The Queen of the Tearling' by Erika Johansen. The entire journey is Kelsea taking possession of her queendom and dealing with its internal corruption and the external threat from the neighboring kingdom. She rarely leaves her own borders; the realm itself, with all its problems, is the stage. The plot is fundamentally about governance and protecting what's already hers, not exploration. It's a very contained, internal struggle, which gives it a specific kind of tension that sprawling quest narratives lack.
For a more literal interpretation, 'The Once and Future Queen' by Megan Morrison is a middle-grade retelling where the entire story is set in Camelot under Guinevere's rule, reimagining her as the active monarch. The walls of the castle and the city feel like the entire world for the characters.