There is a line in a Dorothy Sayers novel that is instructive.
"The first thing a principle does is kill someone."
Now, I think that may be a little strong. But holding principles is almost guaranteed to cause trouble somewhere - otherwise, we'd just call them preferences. One can only make sure that one is standing by principles that are worth the trouble.
Well, I guess I'm going to go off to my room to write that hit song "Alone in My Principles!"
Karen is just fine. Nowhere is she lecturing, chastising, or berating anyone else for doing something differently than what she does or believes. The organizer, on the other hand, is rude, and, depending on what she does next, could veer into ridiculous.
I, too, decline to participate in the Pledge, the NA, and public prayer. I've never said anything about it to anyone, ever. To my knowledge, people don't notice. I will stand respectfully while others do, but it is my personal choice to not take part. There is nothing rude in that. Forcing someone to participate in activities that they do not wish to or are not comfortable participating in, however, is extremely rude. It sounds like the organizer is in a tough spot and may not have the spine to stand up for Karen, and that the third party complainer will likely continue to make this an issue. I hope Karen has a calm reply prepared, and, depending, if the third party complainer continues to complain, it could turn into a civil rights issue.