Youkoso Jitsuryoku Shijou Shugi no Kyoushitsu e S2 - Episode 8 - Suzune Explains

Suzune attended the same junior high as Kushida. That's why Kushida wants her expelled.

Kushida told Suzune and Ayanokouji how she destroyed her homeroom class by telling everyone their worst secrets. Being helpful and friendly gives her access to their current class, so Kushida makes viable threats. Kushida also hates Ayanokouji because she can't find any dirt on him. He's the most dangerous student at school to her. Ayanokouji has his own goals, so he'll find a way to keep both Suzune and Kushida after their wager on expulsion.