I edited the first chapter of the 1939 strand of my story. Again. Amalie's brother dadada da da's a Carlos Gardel tune, Por una Cabeza, and invites her into a last tango.
And here is the original song but no dancing.
But now there's an additional layer of research. While Por una Cabeza was created in 1935, the music by Carlos Gardel and the lyrics by Alfredo Le Pera, that doesn't necessarily mean it was familiar music to Amalie and her brother. So off I go again to research some more.