One of the worst parts of the rape scene was seeing Rumi crying while watching it being filmed. The Fridge Horror comes in when you're given time, near the climax of the movie, to remember that scene: you realize that Rumi may already have been unstable and delusional, but this and the racy photo shoot were the things that pushed her permanently over the edge.
Or even worse, if Rumi was already delusional, she thought she was seeing herself getting raped. It gets worse when you consider just how strongly she protested Mima doing it in the first place and how it connects with the conclusion of the Show Within a Show.
The red dress Rumi as the Real Mima wore during her confrontation with Mima. She said it was new, but maybe it was what Rumi wore when she was an Idol.
The lyrics at the beginning of the film have some Fridge Horror to them. Me-Mania may have gotten some ideas from what the girls were singing.