Mandy does not specifically answer this anywhere that I can find, but the hardest ones for her were the ones when she had to pretend to not be friends with actors she had made friends with off camera (pretend to be an outsider). She also stated in the DVD commentary that she was very uncomfortable doing the scenes in the bus to and from the school where they did tutoring because of the heat and because she was distracted by the neighborhood kids that were constantly visible outside the window. This is one of the scenes where they had to re-loop the dialog because the original was unusable. Also, the scenes where she had to drive were difficult because of the condition of the car she had to use.