Margaret's husband had claimed the crown of France by right of inheritance; Joan of Arc's intervention in the ensuing war helped ensure that Henry would not be King of France. Her marriage was part of a treaty between France and England that brought a temporary pause to that long conflict.
In the Wars of the Roses, Margaret's son, Edward, was the Lancastrian heir; Margaret's hopes for his succession were dashed when her forces were defeated in 1471 and Edward, the Prince of Wales, was killed and Henry VI soon died in the Tower.
Margaret of Anjou appears as a character in four of Shakespeare's plays: all three parts of Henry VI and in Richard III. Shakespeare takes considerable artistic license in her portrayal. She's also been mentioned in more recent stories about the Priory of Sion, popularized in The DaVinci Code, where her father was supposedly the ninth Grand Master of that legendary organization. Historians generally dismiss the organization's existence as a fiction.