You find her in a random encounter in the forest around Gongaga or Cosmo Canyon.
You have to beat her in battle then you go to a place with a save point. Don't save or pause the game or she'll just steal your gil. You talk to her and say these answers:
1) Not interested. talk to her again and say: 2) ....Petrified. I think you keep talking to her and say: 3) wait a second!. 4) .... Thats right. 5) ..... Lets hurry on.