I don't care why you doubt this story, because it's true. However, since you ask, my guess is that you doubt this story merely because it makes you feel better on some level. If you didn't doubt this story, you might have to consider that your perception is wrong. Most people don't like doing that.
Antiguv, I think you have nailed why these pro death people don't want to believe that Terri is suffering. They would rather bury their heads in the sand and pretend she is peaceful and call anyone a liar who says she is suffering. Much easier on the old conscience.