Hmm, on trips where I've travelled with a friend I've always assumed we would share each other's photos. However, I'm also usually the "lesser" photographer -- my camera isn't expensive, and I will forget to take photos of something exciting if I'm too busy watching it instead.
So I guess I've never thought of it from the standpoint of the photographer who doesn't want to share with the person who isn't as good at photography. Normally if I travel with someone, I'm the person who is good at reading maps, good at doing math in my head to convert currency, etc. So I see that as my "contribution" and assume that the vacation turns out vaguely equal. OP, did your friend contribute anything that was helpful to you, at all, during the trip?
I'm also a writer, and if I write anything about my trips I would be happy to share it even if my friend didn't. I wouldn't automatically assume that she would steal my writing and credit it as hers. That seems like such an unfriendly thing to do.
I'm not really understanding the motivation either but now I wonder if I've pissed off my photographer friends in the past.