First, let me say I feel bad for the girl, and not her father. However, from what I've read, it doesn't sound like she killed her father in self defense. That makes it murder, and retaliation. A call to DSS or the police would have stopped the abuse, too.
It sounds like removing such a problematic person from her life gives her a shot, at least, at leading a "normal" life, which is good.
However, she lied to the police about what happened, which is a sign of guilt. People lie to avoid problems. She lied because she knew what she did was wrong.
Still, I feel bad for her, but wish she had found a "better" way around the problem.
Abusers often ingrain in their victims that horrible thing will happen to them if they tell. Maybe a younger sibling will threatened/killed, or another family member, or a pet. When you're in a situation like that, sometimes death--yours or theirs--can seem like the only option.
And I agree that a few years of supervision is a good idea. There are a lot of social and coping skills she's going to need to relearn, if she was ever taught them in the first place.
reunification (with her mother) is one of the goals of court supervision."
Any bets that the daughter's abuse started when the mother fled herself?