Jack Elliott was John Elliot, a Hollywood composer who got his start in Chicago. As noted above, he wrote the theme song for the movie this song first appeared in. He worked with Rogers and Evans a lot so the confusion is normal.

Jack Owens was Roy Rogers' uncle. Mary Ann was Jack Owens' daughter who was ten years old when the song was published. Also from Chicago.

How much help she got from her father and how much the different ASCAP/BMI listings had to do with the politics is up for grabs.

Owens the Elder also wrote the Hukilau Song and the Hut-Sut Song &hc.

Mary Ann Mercer was a staff vocalist at WBBM (Chicago!) where she had a nationally broadcast show called "Melodies of Mary Ann." The sheet music mentioned above was most likely from NBC.