What is the signifiance of the ka'tsina in the story "Yellow Woman"?
There is great significance to what you are asking here. Although the term used in the story is "ka'tsina spirit," it has a lot to do with "the man" as well as "the Yellow Woman."
Quite simply, the man smiles and calls her "Yellow Woman" while suggesting that she WILL come along with him. This is in reference to the previous night where stories were told.
"[She spoke of the] old stories about the ka’tsina spirit and Yellow Woman."
These stories speak of a spirit of the mountains who takes women away to live with him. The evening before, the woman hints that she is Yellow Woman and Silva himself is this mountain spirit or the "ka'tsina" spirit. The difference is that now, the man is living the life of the ka'tsina spirit in his actions as well. Whether or not she wanted it (and whether or not Silva is actually the ka'tsina spirit), she has BECOME Yellow Woman!
In conclusion, it is important to note what a strong draw she has toward Silva. He is virile, strong, and dangerous. Silva also seems deeply connected to the myths, especially that of the ka'tsina spirit. As the story moves along and the journey continues, she is drawn further and further into Silva's grasp.