During the school trip, Sasaki spends most of her time with her friends in group two and leaves the trio to their own devices. Occassionally she would come back to their room to gather her things or to check up on them but, at every visit, they were either hostile towards her or were doing something weird making her decide to stay away from them as much as possible. This feeling of avoidance applied especially toward Tomoko and even continued during school after the trip was over.
Despide her facade smile, she's a bad tempered person. She doesn't want to associate with her school group and especialy Tomoko, since she thinks Tomoko has sexual interests in there. We can notice, though, that she gets even more pissed when she realises in the sport festival that Tomoko had none of interest in her very person, but only in cheerleader uniforms.
Also, when Yoshida hit her while asleep in the school trip ( dreaming Tomoko starting to touch her chest again), she took revenge by marking her entire group as present from dinner time.
59, 69, 72,