Carmelita Spats is the unofficially adopted daughter of Count Olaf and Esmé Squalor and possibly a V.F.D member. She often calls people whom she deems to be lesser than herself (of which there are many) "Cakesniffers", which Mr. Poe takes as a joke.
Carmelita Spats first appears in the fifth book in the series, The Austere Academy, where she is described by Snicket as "rude, violent [and] filthy." The book opens explaining that “If you were going to give a gold medal to the least delightful person on Earth, you would have to give that medal to a person named Carmelita Spats, and if you didn't give it to her, Carmelita Spats was the sort of person who would snatch it from your hands anyway.” Snicket warns that one should stay as far from Carmelita as possible, and Duncan Quagmire tells the Baudelaires that the less time a person spends with her the happier he or she will be.
Carmelita is portrayed as a bully at the Prufrock Preparatory School, where Sunny, Klaus and Violet Baudelaire board, in The Austere Academy. Showing prejudice, Carmelita bullies both the Baudalaires and the Quagmires for being orphans. She uses a staple term, "Cakesniffers," (and once "Saladsniffers", when Sunny falls asleep in her salad) to refer to anyone whom she holds in contempt, chiefly the Baudelaires. Her constant labelling of people as "Cakesniffers" may be a reference to Holden Caulfields' similar usage of the word "phony", given that there are other J. D. Salinger references in the series.
In the fifth instalment in the A Series of Unfortunate Events collection, The Austere Academy, Carmelita first appears as a student of Prufock Preparatory School. Across the book Carmelita always picks on the Baudelaires and the Quagmires with her made up song "Cakesniffing Orphans in the Orphans Shack". She also is given a job by Coach Genghis (Count Olaf) to tell the Baudelaires when they required to attend S.O.R.E. sessions (after which she would snobbily demand a tip). She does not appear again until the tenth book.
In the tenth instalment in the A Series of Unfortunate Events collection, The Slippery Slope, Carmelita reappears as a member of the Snow Scouts, a mountaineering group of which Quigley Quagmire is also a member. At the end of the book, all of the Snow Scouts except for Quigley, who was with the Baudelaires at the time, are captured by Count Olaf. He and Esmé Squalor are able to convince Carmelita to join Olaf's villainous troupe.
In the eleventh instalment in the A Series of Unfortunate Events collection, The Grim Grotto, Esmé starts referring to Carmelita as "the daughter she never had," and spoils her accordingly; both she and Olaf are seen within the book to bend to her every whim. Olaf is less fond of her, and this dislike grows during the book, but is still persuaded to name his submarine The Carmelita, Carmelita having said that The Olaf is a "cakesniffing" name. To outline the degree to which she is spoiled, she is dressed as "a wikipedia:tap-dancing ballerina fairy princess veterinarian" during the book.
In the twelfth novel in the A Series of Unfortunate Events collection, The Penultimate Peril, Carmelita's spoiled attitude appears to have to have been exacerbated under the care of Esmé Squalor. Her attire is as eccentric as in The Grim Grotto; this time she dresses as a "ballplaying cowboy superhero soldier pirate" for the duration of the book. Count Olaf becomes increasingly tired of her attitude and violently knocks her to the floor, ending their already tenuous relationship. She is abandoned at the Hotel Denouement, along with Esmé, towards the end of the book, and it is unknown if she survived the fire that had been set at the hotel; the narration implies that even if she did survive the fire, she never again met the Baudelaires.
Carmelita submits a book about how wonderful she believes herself to be as evidence in a trial against Count Olaf. It is implied earlier that Carmelita herself published this book, entitled Carmelita Spats, Me: The Completely Authorized Autobiography of the Prettiest, Smartest, Most Darling Girl in the Whole Wide World; an excerpt from Page 793 detailing her misguided encounter with a V.F.D. librarian appears in Lemony Snicket: The Unahourized Autobiography where it is listed as having been published by Spoiled Brat Press.