Hopefully adding to a five year old thread isn't discourteous; just wanted to add a reference here to another recording of this song. Helen Schneyer was a guest on the January 27, 1996 episode of Prairie Home Companion and "Lonesome Robin" was the song performed. Listening to the old PHC episodes is actually how I came across this song, and thus this thread looking for more information.

As long as the site remains online (obviously, the content is not mine to control), the show may be listened to here:
https://www.prairiehome.org/shows/58387.html

Garrison Keillor's introduction and interview of Helen Schneyer begins at 18:10 in the audio stream on the site and the song is sung at 19:40.