Mary GrandPré created this illustration, and all of the other original covers. The creative director at Scholastic chose her for the job because they thought her style had a “magical quality,” in its softness. She worked solely with her creative director and not with JK Rowling when designing her illustrations, and so she was able to bring in her interpretation of the story into the design.
In an interview with scholastic, she described this process as the best way to keep their separate creative visions from blending and "getting muddy." She would read the book in its entirety, paying great attention to the details described and the mood of the story, and she would design her illustrations accordingly.