Journey to the River Sea - Eva Ibbotson

Goodreads 4.2

Sent in 1910 to live with distant relatives who own a rubber plantation along the Amazon River, English orphan Maia is excited. She believes she is in for brightly colored macaws, enormous butterflies, and "curtains of sweetly scented orchids trailing from the trees." Her British classmates warn her of man-eating alligators and wild, murderous Indians. Unfortunately, no one cautions Maia about her nasty, xenophobic cousins, who douse the house in bug spray and forbid her from venturing beyond their coiffed compound. Maia, however, is resourceful enough to find herself smack in the middle of more excitement than she ever imagined, from a mysterious "Indian" with an inheritance, to an itinerant actor dreading his impending adolescence, to a remarkable journey down the Amazon in search of the legendary giant sloth.