Margaret of Anjou - The "She Wolf" of France

Margaret of Anjou was queen of England via her marriage to perhaps England's most inept king, Henry VI. She has become famous as the "she wolf" of France, a spiteful aggressive woman who cut down her enemies and revelled in causing pain, but how accurate is this assessment? Has Shakespeare done the dirty on this fascinating medieval queen, or was she truly the evil shrew we've all been taught?