If my boss respects me I will typically keep her in the loop about what is going on. Let her know I'm going to take a shot at fixing the situation, but wanted to give her a heads up about it. Nothing for the boss to fix, just awareness that I'm trying to correct a situation, and if I'm not successful she'll already be aware and ready to take the correction to the next level.

As for the face to face with the co-worker, I'd go neutral but firm. I've had annoying coworkers in the past who, when confronted, seemed genuinely perplexed they were being perceived that way, good long talk about it cleared the air. On the flip side, I have a young coworker right now who is rude and annoying and is very content being that way. Our conversation about the way she interacts with me only served to scare her so now she stays away from me and doesn't interact. Win win!