A couple days after spring break ends, Mom finds out that Via never shared anything about her school's spring play. Mom is uncharacteristically angry with Via about it, and they get in a huge fight. Via screams that she doesn't want them to go, and then things get very quiet. Listening from his bedroom, August can't even hear with his hearing aids.
By keeping this secret, Via's independence has very negative consequences. It's unclear why exactly Mom is so angry about this, but the fact that this situation escalates so much suggests that these arguments are a natural consequence of teens' growing independence.