Here's why:
* What did she demonstrate? We need to know what skill, talent, or knowledge she showed.
* To whom did she demonstrate? Who was the audience for her demonstration?
* How did her hard work contribute? Was her demonstration a result of practice, dedication, or a specific achievement?
Here are some examples of how to improve the sentence with more context:
* "She demonstrated her coding skills because of her hard work."
* "She demonstrated her new invention to the judges, thanks to her hard work."
* "She demonstrated her commitment to the project through her tireless effort."