She taught Antoinette French ceremonial etiquette. Antoinette gave her the nickname "Madame Etiquette".
One day when Antoinette was taught to ride a donkey, she fell off. Her friends went to help her up immediately, but she said, "leave me on the ground, we must wait for Madame Etiquette. She will show us the right way to pick up a Dauphine who has tumbled off a donkey."
Episode 8--Oscar in My Heart probably got the horse falling idea from the incident, and made it more dramatical and had Oscar involved.
She was eventually gullotined during The Reign of Terror due to her closeness with Marie Antoinette.