First of all I will tell her that teachers never want that their student will score low. They always want that their student will progress a lot.
I would like to help her sharing some motivational thoughts to her. I can also tell this situation to her parents so that they will do something. According to me if a person want to get over his disappointed he first learn something from his mistake and accept it and must have a strong spirit which let him do best in the future.
Well she can improve her grades by doing his hard work. May be she has also done in the past but now she has to increase it. She should learn all the notes at the end if the day. She may use past sample paper to do best in the next exam.