Ella being in Hasta La Vista at final jam does not make sense.

I know it was released in 2008 and its 2015 and I know its a kids/teen movie but something about this should have been picked up and said ages ago but Ella being in Hasta La Vista at final jam does not make sense.The reason it does not make sense as the whole movie depicts Ella practicing with Tess and Peggie all summer for final jam and it is not until back stage at final jam that they split and go their seperate ways.So she would not know the dance routine and song lyrics to the song unless she is a fast learner of dance routines and song lyrics yet again the movie depicts her not being able to do that as again backstage Tess tells both Peggy and Ella to pick up the slack and dont mess up as they still dont have the routine down yet there she is and she has got evrything down as well no cock ups what so ever I know it was filmed that way I am just saying it does not make sense and she should not have been in there at all.