However, in the original series, Jilly Gordon clearly is. When the plague hits Ashleigh's family, various horses who survive or are sold before the first book, die (Midnight Wanderer, for example, who is put to sleep in the book, 'Goodbye Midnight Wanderer', apparently dies of the mysterious plague, rather than from the accident.)
In the original series, Jilly Gordon is a horse that survives or is sold before the first book. When Ashleigh's family is struck by the plague, several horses who survive or are sold before the first book die (Midnight Wanderer, for example, who is put to sleep in the book 'Goodbye Midnight Wanderer', apparently dies of the mysterious plague rather than from an accident.)