It feels just a tad weird having everyone at school suddenly into idols a lot, when she was bullied in the beginning largely for following an idol.(kinda like if a manga had a kid bullied for being an Otaku, and suddenly the whole school are major manga enthusiasts)
But perhaps this is just a culture difference, and Idols are bigger than I imagine them to be.
I definitely am familiar with there being sports team rivalries when I was in school. And definitely there were the fans of celebrities.(I lived through the twilight team vampire/team wolf shipping wars).
That said, having her bullied because she was a fan of a rival idol group is actually a great development. Bullies don't need a reason to choose victims, but a fandom rivalry certainly could be enough to get the ball rolling.
And the bully having social power as well as the backing of a administrator, certainly could influence people to only support her group publicly.
Anyways, thanks for the translation! I look forward to the future developments.