Peaceful, yes. Illegal, too.
This is where the starving dog analogy falls apart. Dogs can be euthanized. People can't, even at their own request in the end stages of a terminal illness. Doctors are so afraid of seeming to do so that end-of-life care frequently excludes pain-killing medications for fear that the patient's breathing may become too depressed for him to continue to do so. We prefer suffering in this country. We think it makes us better people.
I disagree, but that's another discussion.
As for Mrs. Schaivo, according to the overwhelming concensus of physicians who have actually seen her, the body she once inhabited has no mind to need peace. The peace we discuss here is actually speed, and that would be more for the sake of the living.