Lise bullied in school, its the scene where Theo internal monologues more about their past. Because the stasi started targeting the Hohensteins and making it hard for them to live, people stopped wanting to be associated with them for being on the stasi's bad side. Lise became ostracized by many of her peers in school and severely harassed. The dirt marks on her school uniform and hand there were from dirt clods that they were throwing at her. They mostly went after her instead of Theo because she's the easier target. Also even before that she started getting shit from some other girls who wanted Theo for themselves and saw Lise as an obstacle to that because of the rumors going around school that she and Theo were fucking since they never dated anyone else and were really close, going everywhere together and seeming like a couple, ect. So they'd spit in her face and go after her to tear her down in anyway they could.