My personal decision:
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She died 15 years ago. Let her go already!!! But at least over medicate her and let her go with the same peace and dignity that we give to animals and criminals instead of starving her.
I am not religious at all. For you religious people lets handle this with as much logic as your religion will allow. Pull the tube and let God decide. If God wants her to live, she will, and it will be a miracle (and turn me religious overnight!) If she dies, then God is the murderer and our hands are clean. If it's still our fault somehow, ask for God to forgive you and all is good. There is also the argument that it was God's will for her to die and we are intervening.
There is also a clear cut distinction between 'killing' and 'murder'. Murder is killing, but killing is not murder. Killing someone in self defense even though you know killing is normally not acceptable, you have exhausted all other means and resort to killing as a last resort, and you know you would not do it in ordinary circumstances for example, is not murder.
In this case, you can't murder someone who is for all intents and purposes, already dead. Acting with someones wishes and interests in mind to kill that person, is not murder. Suicide is not murder. Our bodies are the most important piece of property that we have, and like anything else, it is our right to exercise our free will with regards to our life and propery so long as it doesn't trangress on anyone elses rights to the same.
In this case we don't know what her wishes are, so we can't say if it's murder or not if we allow her to die.
The husband doesn't sound like that great a person and my decision is in no way influenced by his wishes. On one hand you could say he wants her dead so he can get her money, but on the other it's unreasonable to believe that when this first happened in 1990 that he saw large sums of money come to him for it to keep her alive until then. You could say he isn't a loving husband because he denied treatment after he got money, but you could also say that this coincided with realizing that her parents are delusional in keeping her alive at all costs and he finally woke up and decided to just let her go. Just about anything involving this man is at least three sides. Then you have the sudden memory of her wishes 8 years later, but you also have him telling his mistress that they never talked about that back then. I would lean on the husband being a non credible asshole myself, but again, my personal decision to let her die is in no way influenced by the husband.
The parents, as said before, are selfish and would rather their daughter live in hell like a chopped up lab rat than suffer any moral guilt. I would gladly bear the sacrifice of a lifetime of guilt in exchange for peace for my child.
If I were a judge:
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Considering everything, there are two many sides to any point that can be brought up, so the parties involved have turned to the government/law/constitution.
In our Constitution, everything is based on presumption. We have presumptions of what is normal and pre-existing, and guidelines for when we should act contrary to what is presumed. In criminal law for example, we are presumed innocent until proven guilty; and the death penalty is not administered in cases with any, however small, reasonable doubt; etc. Even the Constitution itself is written on the presumption that government has no power except what is explicitly granted by the constitution (in theory anyway). In other words the constitution favors what is presumed to be the every day norm unless extraordinary circumstances cause us to favor contrary to the norm on a case by case basis.
It is the duty of any judge, law maker, or politician to enforce the guidelines outlined in the constitution even if they conflict with personal values.
Such should be the ruling in cases like this in favor of what is already presumed, the preexisting condition being life, unless proven otherwise beyond reasonable doubt that she would have wanted to die.
Edit/Add:
Also, in comprimising with the wishes of both parties:
1) Absolve the husband of further responsibility, and revoke all associated personal financial gains due to this situation; grant or recommend formal divorce.
2) The parents, who want to keep her alive, shall bear the full burden of the responsibilities and costs associated with doing so. If this is too expensive, I'm sure all the protestors that wish to keep her alive are more than willing to contribute for continuted medical expenses....