I read a book in the USA in the late 60s or early 70s that I've never been able to re-locate. I believe it was set in the 1930s, and may have been written then. It's about a very tall teenaged girl who's travelling with her father in a circus freakshow as a Giant Girl. As part of the act, she sings. She has an unusually powerful and beautiful voice, and is heard by a scout from an opera company. At the end of the book she decides to leave her father and audition for the opera company, and is accepted. The book had a very sad tone to it which seemed unusual for children's fiction at the time. I'm unable to remember the title, author, or characters' names, just the plot.