If we accept the thesis that the incident in the cabin was a violent incident, but to me it looks like she started a personal vendetta against Nika because Summer left her for him only when Summer disappeared, I suspect that she treated him very badly then, which led to Nika started having attacks of aggression, which eventually led to a violent incident. Then she felt guilty and convinced that it was because of her that she had changed. Summer disappeared when Nami was 14, bad Nami was at 15, 16, Nami as we know her is 17, 18 and 19