From some of Sheehans speeches, I'd day she holds all America is great contempt and hates it. That doesn't make her a communist, just a seditious whiner with serious emotional issues.
I highly doubt that Fox News did anything besides quote Sheehan accurately. The fact that this moonbat letter-writer is implying that she was overtly called a communist indicates, to me, that the leftists know she is not appearing well to the average American. Why else would she try to defend Sheehan against a charge that hasn't been spoken? Not to mention that the moonbats just hate being exposed for what they truly are, even if they are not being expressly labeled.