This came up as a animal Ark Hauntings, It has on it Animal ark where animals come first but I don't see hauntings on it.
When Mandy meets stuck-up Susan Collins she quickly decides that the only good thing about her is her pony prince. But then Mandy realizes tha Susan's determination to win at show jumping threatens the life of the beautiful pony.
This is the Scholastic reprint of the Animal Ark series book. No where on the book (either on the original Animal Ark Pony on the Porch which my son has or on this reprint) does it say that it's one of the Hauntings series books.