Nash, don't you get it...they're not really arguing about what's right for her. They're demonstrating the classic human psychological trait of refusing to concede their point. I guess we're all doing it to some extent.
Yet, at some stage, we have to say to 'ell with our own beliefs and with what her husband and parents want and decide what's best for her. Refusing to concede the issue will only cause her to linger on endlessly in a mindless purgatory, which would be a position that gives the lie to our protestations of compassion.
A couple of decades ago, a young man and his father stopped their car in a small patch of woods on some property they were thinking about buying. Unwittingly, they stepped from their vehicle into a pool of unseen gas that was leaking from a pipeline nearby.
Something set it off. In the ensuing conflagration, the father burned to death and the son suffered third degree burns over his entire body.
An ambulance eventually arrived and took what had once been a normal human being to the hospital. The hideously burned victim still possessed a fully functioning mind and was able to communicate with his family and doctors. He pleaded with them to let him die.
The physicians and burn specialists refused to listen to his pleas. With fingers melted together, no hair remaining on his body, vestigial ears, and suffering unbelievable torment, he begged to be allowed the relief of death...and he was refused.
Years later, after extensive treatment and plastic surgery, he was released to try to rebuild his life. In an interview on Nightline (Hope my memory hasn't failed me) his physicians acted as if there was nothing else that they could do...as if forcing him to live was somehow more humane and compassionate than simply allowing, or assisting him to die.
The young man has attempted to rebuild his life, but he did it not for himself but for those around him. He has a job, but with horrible burn scars over his entire body, he will probably never be married and is unable to have children.
Asked about the doctor's decisions to move heaven and earth in order to save him, in light of events that happened later, the young man told the interviewer, "They should have let me die."
So you see, I find the reasoning behind some of the arguments against allowing this girl to die to be more about one's own need to dig in and defend a nebulous "principle" than about what's right for her.