I question her truthfulness, too. I heard her say on CNN that she decided "Bush lied" about why we went to war after she read the 9-11 report, Dulfer report, Intelligence Committee report and possibly the Kaye report. I do not believe for one minute that she read any of these reports. Perhaps she read the NY Times headlines ABOUT the reports. Because if she'd read the actual reports, she would have seen that all of them say Saddam was on his way to getting nukes, even if he didn't have them now, and that the sanctions were eroding and would soon be gone, and then it would be open slather for him.
Sheehan has allied herself with some very incompetent and ignorant political operatives (the Democratic Party).
She probably very well believes 90% of what she says, except that she alters the point of view, tense, and details to give her statements more authority.
You see this phenomena at large car accidents, fires, natural disasters... People exaggerate their role, or the extent of their first hand observation, and eventually the story where they filled in the blanks becomes more practiced and eventually it becomes as real as fact to them.
I say she's being artificially reinforced, with a lot of very rich and influential people giving her emotional and intellectual vindication, by the very fact that they appear to be taking her seriously. Couple this with a lot of bad information, incomplete facts, and inherent bias within herself and in her preferred sources, and she becomes exactly what is now.