Have you ever thought there may be more to the story here? Why does you coworker feel the need to avoid this person? Did this nurse speak directly to you in this manner? If not, then I would say that it's your coworker's responsibility to handle the situation, not yours. Maybe it's not the nurse who has the problem, but that your coworker just doesn't like this particular nurse or has had a disagreement with her. I would think about things like that before I went up the chain of command. Especially if, as you said in your post, she wasn't rude to the patients.