User blog comment:RumbleXRumble/Neon Nostrade Theory/@comment-14902757-20130910024926

I think it's a genius ability. She didn't have to learn how to do it, she simply got inspired and then was able to start telling fortunes without practice or training. Her ability also appeared to require no training or physical/mental exertion. Also, refer to the "Genius" section in the article dedicated to Nen.