The Bible deals with sin and our fallen state. It mentions forgiveness, but it never, ever says that the consequences of one's actions should be erased just because they've been forgiven. In fact, I think the Bible actually told Christians to do the opposite. Obey the authorities, submitting to consequences of your actions. If you do wrong, then you can be forgiven, but that doesn't mean you escape worldly justice and don't have to face the consequences. The Early Christians were breaking the law by refusing to worship Caesar, and yet, while they broke the law, they still submitted to the consequence of breaking that law.
Render unto Caesar what is due to Caeser. This is about justice and consequences, that isn't connected to Christian forgiveness. We need to forgive her and pray for her, but that doesn't mean she gets a get out of jail free card.
How about a victim of incest? How about a victim of incest who kills the one abusing him/her? Two wrongs do not make a right; however, the US legal system can take into account crimes committed under duress, under fear and under intimidation. If a woman killed a relative who committed incest, should she rot in a jail cell? If a woman killed her own child conceived due to incest, does she deserve the death penalty?
The justice system should have something in place to determine "just kill". So if someone is committed of murder, they could then proceed to a trial that determines if it was a just kill.
Also no, if you kill a child that is a result of incest, you are a murderer and belong in prison. If a woman has an abortion just because she was raped or it was due to incest, it's still a baby that is being killed. (I would argue the mother that had the abortion doesn't belong in prison, but here we are talking about a 2 year old girl, that goes beyond abortion)
It goes beyond abortion, how so?
I don't believe women that have abortions should be put in prison for doing so. That doesn't mean I don't value the life of the aborted child. But if a mother (or anyone else) deliberately commits filicide against a born child, then that mother belongs in prison.
Think about it, the unborn child doesn't have a voice, sadly, the woman that has an abortion often doesn't realize she is committing murder. But in a case like Casey Anthony, her daughter is clearly, CLEARLY a living human being that is alive, intelligent and breathing. Her daughter could look her in the eyes and cry "Mommy, Why?" and ask her mom why she was hurting her...
Casey Anthony knew, beyond a shadow of a doubt that she was killing a child. Whether or not it was due to incest is irrelevant.
-Think of it this way... Women that have abortions are told by doctors and by society that the child in their womb is not actually a child, it's just a fetus, and therefore it isn't wrong to terminate it. So a woman who becomes impregnated due to incest or rape is more likely to have an abortion because she has been taught to think that it isn't a human being yet.
-However, women who have had a child, and it has breathed it's first breath, cried its first tears, seen light for the first time, women who have these children know, beyond a shadow of a doubt that is a living, breathing human being just like them.
In both cases, it would be murder of an innocent human being. But there is a difference, because in one case, the person may not realize that the fetus (who doesn't have a voice) is a living human being. But in the other, it is absolutely clear that it is a human being.
Unless Casey were insane, there is nothing that could excuse the murder of one's own child.