Does mercedes gabung the other glee club ?

I think she did.

Yeah, probably.
I mean, I think she didn't go to Shelby for nothing ...

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.

SPOILERS!

From 'Asian F', anda can see she told Shelby that she wants to gabung her glee Club. From spoilers of the upcoming episode, the Sugar Motta glee Club, the one Shelby is directing, is called Pot of Sugar & anda will see Mercedes and Santana forming part of it.

Yes she does after she feels that Rachel is stealing her spotlight and that Rachel is getting too much special treatment.