Well, having just worked up the courage to sort through this thread... good grief is it long, I have to say, I really think that it is bad form for Camilla to attend this service. Even if her step children, ie the princes, want her to, I think that it can do her public profile no good. Whatever the reasons for Charles and Diana's breakup she did have a role in it. I am not saying that any party was an angel, because none were, but I think that in this case, she should just keep a low profile.
It will be too much for some people, who will undoubtedly say that she is spitting on Diana's memory. Not to say that she is, but were I her, I would not go.
Her going is just not kosher in my opinion. Diana held a lot of animosity towards her, for whatever reason, and did not consider her a friend. IN ANY situation, I think that the people who honor your memory at such a service should be those who cared for you in life, and for whom you cared as well.
Just my opinion though.