A Company of Swans by Eva Ibbotson

Weekly ballet classes are Harriet Morton's only escape from her intolerably dull life. So when she is chosen to join a corps de ballet which is setting off on a tour of the Amazon, she leaps at the chance to run away for good. Performing in the grand opera houses is everything Harriet dreamed of, and falling in love with an aristocratic exile makes her new life complete. Swept away by it all, she is unaware that her father and intended fiance have begun to track her down...