Emma's River — Alison Hart

Emma, her pony, and her mother travel up the Missouri River on a steamboat to join Papa on the frontier. When she sneaks to the main deck to check on her beloved pony, she finds Patrick, a stowaway, who s bunking with her pony, and the two make a deal that evolves into friendship. When the Sally May explodes in a fiery blaze, Louisa, Mama, Patrick, wealthy cabin passengers, poor immigrants, and one plucky pony must find a way to survive the disaster.