She might meet new characters. For example, she could interact with other fighters from different planets. This would add an interesting dynamic to the story as she discovers different fighting styles.
Well, it's possible that Videl gets some special power - up during the Cell Games in the fanfiction. She could be exposed to some sort of energy that enhances her abilities, allowing her to participate in the battles more effectively than in the original story.
In the fanfiction, Videl could have a significant role in the Cell Games. Maybe she finds a way to boost the morale of the Z - fighters, like giving an inspiring speech. This would be a great addition as she is a strong - willed character.