Complex sentence: Policeman's dam Indianapolis failed to win a race but came from a good family, being a great-great-grandaughter of Myrobella whose other descendants have included Big Game, Chamossaire and Snow Knight.
Split into simpler sentences: Policeman's dam Indianapolis failed to win a race but came from a good family, being a descendant of Myrobella. Myrobella's other descendants have included Big Game, Chamossaire and Snow Knight.