First, it wouldn't be a case of dancing on his grave if this really were a "wrong war for bad causes." It's not that, of course, but for those whose war "news" comes from the MSM, her protest might seem to have merit. So you need to focus less on her personal motivations, and more on this particular aspect of her protest.
Second, you might want to mention that members of her own family have asked her to STFU. This would strengthen your case for saying she's acting in opposition to what her son stood for.
And, of course, there's the likelihood that Ms. Sheehan is a willing dupe for the Michael Moore types who are pretty shamelessly exploiting her grief to further their own agenda. Wouldn't hurt to toss that in, too....
When she personally is quoted as saying that America is not worth dieing for and equally bad anti-American themes, she sullies all her own son fought forand gave his last full measure of devotion for, and gives aid and comfort to the very enemies who killed him IMHO.
That is what pushed me opver the edge and got me to write the letter. I do not believe she is a dupe in the least.
...and, so I believe that her activities need to be exposed so others can be educated. I believe if they are, they will see it as repugnant as I do.
Just my thoughts on the matter, thanks for your own.