Complex sentence: Her son Janissary (sire by Isonomy), won the St. James's Palace Stakes and sired the 1898 Derby winner Jeddah whose mother was Jannette's racecourse rival Pilgrimage.
Split into simpler sentences: Her son Janissary (sire by Isonomy), won the St. James's Palace Stakes and sired the 1898 Derby winner Jeddah. Jeddah's mother was Jannette's racecourse rival Pilgrimage.