A Pony in Trouble by Jeanne Betancourt

Pam's father is a veterinarian, so she is used to being around sick animals. But when her own pony gets sick, Pam needs her Pony Pals more than ever.Her Pony Pals, Anna and Lulu, try to figure out what is making the pony sick. Can the Pony Pals solve the mystery? Will Lightning the pretty pony, be a pony in trouble for long?
 
- Goodreads Summary