What does 2 Chronicles 23:13 mean?

She looked and saw the king standing by his pillar at the entrance, with the commanders and trumpeters beside him. All the people were celebrating and blowing trumpets, and singers with their instruments were leading the praise. Athaliah tore her clothes and screamed, 'Treason! Treason!' 2 Chronicles 23:13 - Modern Text Bible

(Athaliah realizes she's been overthrown. She reacts with outrage and accuses everyone of betrayal.)