Fanny is one of the 2 antagonists of the fairy tale "Diamonds and Toads" by Charles Perrault.
She is the older daughter of an ill-tempered widow, and she is just like her mother in terms of personality. She hates her sister and she and her mother mistreat her. She is also very rude and disrespectful.
One day, the younger daughter helps an old beggar woman at a well. The old woman, who is really a fairy, blesses her with the gift of having jewels and flowers fall out of her mouth whenever she spoke. When she returns to her mother, the mother becomes jealous and wants Fanny to have he same gift.
Fanny is sent over to the well the next day. This time, the fairy disguises herself as a beautiful princess. Despite this, Fanny is still rude to the fairy. The fairy curses Fanny to have toads and snakes fall out of her mouth whenever she spoke.
When Fanny comes home and explains to her mother what happens, the mother blames the younger daughter and throws her out of their home. The younger daughter is eventually rescued by a prince, who marries her, while Fanny ends up driven out by her mother, and she dies alone and miserable in the woods.