She's just being overdramatic

When the Asano twins were seven they made a promise.

"It's just us now," Gakushuu said firmly, holding her hand tightly. "We can't rely on mom anymore and we can't trust dad." His gaze narrowed. "So we have to rely on each other." He gripped his sister's hand tighter. "We can't trust anyone else."

Mitsuko was hesitant, but the smash from downstairs made her flinch. "...Just us?"

"Just us," he reiterated.