Jamieson, Fausset and Brown on 2 Chronicles 22:10

10. Athaliah ... arose and destroyed all the seed royal--(See on 2Ki 11:1-3). Maddened by the massacre of the royal family of Ahab, she resolved that the royal house of David should have the same fate. Knowing the commission which Jehu had received to extirpate the whole of Ahab's posterity, she expected that he would extend his sword to her. Anticipating his movements, she resolved, as her only defense and security, to usurp the throne and destroy "the seed royal," both because they were hostile to the Phoenician worship of Baal, which she was determined to uphold, and because, if one of the young princes became king, his mother would supersede Athaliah in the dignity of queen mother.