Rhythm in the Clouds (1937)

Struggling songwriter Judy Walker talks her way into the apartment of a famous composer, and finds that he's on vacation. Homeless and without any money, she decides to stay at his place until his return, making use of all his belongings, and spreading the word that she is the composer's collaborator. She writes a song, wtih the composer listed as the co-writer, which becomes a big radio hit. The famous composer returns, and screwball comedy ensues.