I heard the song is about MA Jones going to promote union organization in the coal mining camps in the Appalachians. I think she also organized in cities. At first the railroads, who also owned the mines or vise versa, let her ride, often for free she because she was an old lady. But when she became so popular, they refused her passage. So she had to sometimes find other means--horses--to get into the camps--must have been some travel on those mountain roads. Taking a more interpretative view of the song. White horses for much of our mythology have been the mode of travels for heros or heroines. And in rural poor American, a chicken dinner was often a luxury, reserved for Sunday, especially if the preacher or some other important person were coming. A chicken may have been the best meat available and such a dinner would have been a sign of respect. I hope someone else can either add to or correct this brief reply.