Queen Margaret is the widow of King Henry VI, the same character as the Queen Margaret of the Henry VI plays.
Though exiled, she returns to England to witness the destruction of her enemies. Half-crazed by grief, she ritually curses all those who stood by as her son was murdered and did nothing as well as those who did the deed and those who profited. She refuses to acknowledge any of her own crimes (see the Henry VI plays) and concentrates instead on the people who hold the power she has lost. She ends up almost befriending Queen Elizabeth once the latter’s woes come to match her own. Her hatred seems to be all that keeps her alive. She is often more a chorus figure than an actual character.