Margaret of Anjou became Queen Consort of England when she married Lancaster King, Henry VI. Although from very noble lineage, (Margaret's father was not only Duke of Anjou, but he was also titular King of Sicily, Naples, and Jerusalem), she was pretty much without wealth. The fact that her parents could not provide a dowry for her marriage to Henry VI meant it had to be kept secret, unless the Lord's of the of England revolt in protest against the match. Royal brides should bring something of value to the table after all. However, the English King desired the match. When they married she was fifteen years old and he was 23. She may have been beautiful, but she was not the ideal beauty of the time. During these times, plump, curvy, well endowed women were desired. Margaret's nickname was "La Petite Creature." Also golden hair was also valued, and Margaret despite what some pictures show her as, could have been darker like Mediterranean people tended to be.
Regardless of her looks it was a well known fact that she was a very educated, strong willed, and had a dominating personality. This was in many ways both admired and hated in her, (or any Queen for that matter). The thing was, Henry VI was weak and overly zealous when it came to his religion. Also, he suffered from bouts of insanity just like his maternal grandfather, Charles VI of France. Henry VI's father, Henry V, was a great soldier and leader of men; everything his son who succeeded him was not. Henry V, famously ended the Hundred Years War with France when Charles VI's Queen, Isabella of France, was forced to relinquish the crown to him upon her husband's death and married her daughter, Catherine of Valois to him. If Isabella of France was blamed for giving the Crown of France to Henry V of England, then Henry V's son's wife, Margaret of Anjou was blamed for giving the French crown back to the French... Ironic? Maybe...
Margaret only produced one son with Henry VI. Soon after Prince Edward was born, the King slipped into complete madness. Immediately a fight for power ensued. Lancasters against the Yorkist Plantagenets. The Lancasters had for their sigil a red Rose, the Yorkists a white rose. This bid for power turned into what was famously known as "The War of the Roses." The Lancasters, of course supported the King and Queen, for the King was a Lancaster. The Yorkists supported the powerful and wealthy Plantagenet Lords who ruled before the Lancasters. During her time as Queen, Margaret was always fighting with the Duke of York for control over her husband.
During this civil war the Lancasters were defeated and Henry VI taken prisoner by the Duke of York. The Yorkists now had the King in Check and under their control. However the Lancasters in turn defeated the Yorkists and re captured the King. The Queen could no longer pretend the King's disabling madness was only temporary, she quickly seized power for her infant son, Edward. If the King was unable to rule then the crown would go to the Prince and as he was only a child, she his mother and the Queen, would rule as regent. People did not like women rulers back then so they did not make it easy for her.
In order to raise money for her armies, Margaret sold some key pieces of Land in France that made it possible for England to keep control of the French. She lost some strategic ports. She lost many brownie points with the English people and lost the French crown just as quick as it was won by her husband's father. She earned a lot of hatred for this folly and gave substance to the stereotype that women make terrible rulers. Also, this made Margaret seem disloyal. She was French after all, and this move made her seem like she had only cared for France's interests, not England's.
There was a period when England had two Kings, Edward IV (Plantagenet), and insane Henry VI (Lancaster). Once again Henry VI was a prisoner of the Yorkists and Margaret was forced to flee into Scotland with her son. It wasn't until Edward IV angered some powerful lords in England, that Henry VI was restored (or more like Margaret was restored) to power. As she returned to England they were attacked by Yorkists and the Prince was killed. Shortly after, it is suspected that Henry VI was murdered. The Yorkists now had complete undisputed control, (for a time), and Edward IV was the only King of England. Margaret was taken prisoner, but was eventually thrown back to France. Her power snuffed out completely.