When Alex is in the hospital room with the patient that has the measles, another nurse in a purple gown is in the room with her standing the corner of the room. She is shown twice throughout the scene standing in the corner, but near the end of the scene the nurse just disappears from the room. There is no way she could have left the room since Alex and the patients mother were standing near the door talking throughout the rest of the scene and we would have seen the nurse leave.
After Iris attacks and kills the young couple the woman can be seen breathing when they are both laying on the floor.
When the Principal runs to the administrator's office and collapses, Nurse Leena runs to him and says "I'm going to move your hand now" but both hands are already off to his sides.