Anne Hyde nearly became Queen of England but died before her chance to. She was a commoner who, through good luck, became the mother of Queens Mary II and Anne.
Catherine Gonsalvus was married off to a "freak" as a joke, but probably had a happy marriage, despite European royalty treating her family like animals.
Marie de Bourbon became Duchess of Montpensier when she was just two years old, and the French royals really, really wanted and needed the girl's money.
Tarabai was a very important figure in history. Without her, there may never have been any Rajas of Kolhapur, and perhaps no long-lasting Maratha Empire either.
Marina Mniszech, known as Marinka the Witch, was the wife of an impostor and ended up becoming the cause of his downfall and her own brutal end.
Louise Élisabeth of Orléans became Duchess of Berry at the age of fifteen, then proceeded to do whatever she wanted for the rest of her very short life.
The hardest task for a royal mistress was getting the public to actually like them. Nell Gwyn made that seem almost too easy. She also has a monument in London.
Henrietta of England, known as Minette, fled England at the age of only three, then became a very unhappy duchess, followed by her very mysterious early death.
Hortense Mancini was quite an interesting lady. She had a husband who knocked out female servants’ front teeth, she ran away from him, and became a royal mistress.
Lettice Knollys was the wife of a guy named Robert Dudley, whom you may be familiar with, but she did way more than just marry him. The poor lady could never catch a break.