User blog comment:IamJakuhoRaikoben/Chapter 261: The One Magic, Review./@comment-2106167-20111125192436/@comment-16344653-20111125195945

maybe Mashima will make them fight in groups of four in some stage of the tournament:
 * Team Natsu: Erza, Lucy, Gray and Natsu
 * Thunder God Tribe: Laxus, Freed, Bickslow and Evergreen
 * Take Over Siblings?: Mirajane, Elfman, Lisanna and maybe Cana. Which is probably why she is training with them