The nurse came to check on Michael after his visions of Libby caused him to scream. The nurse attempted pleasant conversation with him. She explained that he was found badly hurt with no identification, only his letter to Walt. She asked if she should call Walt, and Michael shook his head.
Although being an unnamed character, the nurse is in fact named, as her name is shown on her staff badge. However, her name is unidentifiable in the episode. Therefore, she is considered as an "unnamed character".