if Yuka actually wanted to be by Nanase's side happily, the right and responsible thing to do is to grow some backbone and tell those stupid girls from Ruri class to stop looking down/belittle/fearing the girls from Ai class
No, she should not have to actively take on the entire school in order to be with another person, be it as a friend or a lover. There is a difference between "I associate with whoever I want, not who you say is ok" and "I demand that you stop being elitists, or else".