Kara Borden had better make something very special out of her life. Whatever her degree of guilt, she'll need therapy, as will all her siblings, for a long time. The family will resent her, perhaps even blame her...naturally. Still, she's only a kid and that explains everything. Adolescents' brains don't fire the way adults' do. Terrible tragedy, for the shooter's family, too.
If she wasn't involved in her parents murder and survives this I she may do good things when she grows up. She may even be able to help other girls. Only time will tell and there are a lot of ifs.