Other mistake: Right after Britney visited her mother, she goes into the washroom and cries. The lightswitch in the washroom is "off" and even if there was a window in the ceiling - it was raining outside. So how is it possible that there was light in the washroom above the bathtub?
Toward the beginning of their drive, while the girls are singing "Bye, Bye, Bye" the position of the window behind Mimi keeps changing. Sometimes it is all the way up, then it is part-way down, then back up again.