In the island
Due to the ingestion of Medusoid Mycelium (possibly)
Friday is a right-handed seven year old girl and is the only child on The Island with the ability to write. She wears a white seashell around her neck in which she keeps her cordial. She may have more of a free spirit than the other islanders, as shown when she walks into the camp wearing sunglasses (which are outside the strict dress code because Ishmael believes they can be used as a weapon). At the end of the book, she rides off in a boat with her fellow islanders and it is implied that she met her fate.
Like her father, she is named after a day of the week (notably the one after her father's name).
Friday's only appearance in the series is the thirteenth book; or The End, a reference to the unlucky date of Friday the thirteenth.