Dear Ms. Weathersbee,
Ms. Johnson was probably singing "Dixie" for the same reason that Abraham Lincoln sang "Dixie". It’s fun to sing, and was one of Lincoln’s all-time favorite songs. It may also be one of Ms. Johnson’s favorites. Since you’re right there with her, did you ask her about it? What did she tell you?
In the meanwhile, there’s no need to put words in the mouths of blacks or whites. Read "the Slave Narratives".
Have a nice day,