Schizophrenia is not caused by traumatic events from childhood. Most shrinks think schizophrenia is caused in one way or another by parents and their parenting methods. Curious how the sister got better after Tom goes through the catharsis of unloading the trauma. Reliving the trauma by vocalizing it would be a technique for working with PTSD.
Henry and Lila were far from good parents, so you just gave a good reason to believe that maybe she did have schizophrenia. But yeah, revealing the past won't just cure a chronic ailment like that.
I got the impression that Savannah was schizophrenic long before the attack. She showed signs of it when her mother had a stillborn baby, and Tom wakes up to find her holding the dead baby in her arms. The book details this even more. The attack just made it worse. I didn't feel Savannah was 'cured' by the revealing, but the mental tumor had been revealed and could now be worked on. No therapy was going to help her at all until this issue was acknowledged.
"I'd say this cloud is Cumulo Nimbus." "Didn't he discover America?" "Penfold, shush."
Schizophrenia is characterized by disordered thoughts and perceptions (i.e. delusions and hallucinations). The guy who think he's being monitored by little green men through his TV antennae has schizophrenia. The sister seemed severely depressed and traumatized rather than schizophrenic.