I'm more thinking she'd over blown the audition tape (yes it's awful, it's astonishing Chris said those things but then maybe he was after attention/screen time) - I do think Brook overplayed the shock, horror, disgust for screen time ... and that phoning her sister bit, that hasn't happened before mid-screening, has it?
But I think it's clear why that huge personality change happened after a few days away, where she went from Bubbly Brook to Brook the Bitch.