So, I'm on episode 4, without spoilers, can you tell me if others can see her? It's kinda confusing to me.
In episode 5, you (the viewer) learn that the class is ignoring Misaki as part of a "countermeasure" to ward off the calamity that affects class 3-3 (which is what causes all the paranormal phenomena you see in episodes 1-4, e.g. the girl nearly getting crushed by the falling glass pane; the nurse in the crashing elevator; etc). The basic idea is that the class has one more person than it should (you find out why in episode 6, I believe), and so by pretending that one of the people in the class doesn't exist, they bring the number of people in the class down to the correct number.