I'm quite sure that she is playing for another team, I saw it in the last part of "Asian F". I think it's Shane( I don't know if this is her bf's name) who persuaded her to do so.
From 'Asian F', you can see she told Shelby that she wants to join her Glee Club. From spoilers of the upcoming episode, the Sugar Motta Glee Club, the one Shelby is directing, is called Pot of Sugar & you will see Mercedes and Santana forming part of it.
