What were the circumstances of Thisbe coming to be Madame Sylvie's personal servant?

When Madame Sylvie turned 70, she decided that since she could not go to France and her son scandalized her by taking up with a cabaret performer, she was going to live her life in comfort. She went down to the slave quarters. She saw a girl that she decided would do. She named her Thisbe and took her with her.