This may be a dumb question, but will Diana be there? (At the Rally, I mean; not necessarily the party.)
I don't know. That's a question for her campaign. My guess would be "no." The Irey campaign and the Boot Murtha effort are and must be by law separate entities not in coordination with each other. (Although obviously they are working toward a common cause - Murtha's defeat)
I personally wouldn't risk her presence there, just from the "How would it look?" perspective. But I honestly don't know the laws.