You may get Yuffie at any time of the game...But I suppose you should get her early in the game because she is very useful in boss battles. Plus her limit breaks are worth your time. As, I was saying...She is helpful in the Materia Keeper battle because of her "Healing Tranquil," (For those who don't know, that is Yuffie's 1st level, 2nd limit break) in the middle of the battle. Plus, Yuffie is funny as hell! :)
