Final answer:
The editor-in-chief of an international fashion magazine is the most likely to meet with a celebrity fashion designer for a collection preview due to their influential role and need to obtain exclusive content.
Step-by-step explanation:
The media representative most likely to meet with a celebrity fashion designer to preview her Fall collection in July would be the editor-in-chief of an international fashion magazine. This individual has the appropriate editorial authority to feature upcoming fashion trends and collections in their publication and ensure global reach. They also have a strategic interest in acquiring exclusive previews to stay ahead in the competitive fashion press industry.
On the other hand, an art director of an online fashion magazine is more concerned with the visual representation and may not have the same clout or need for early previews. The author of a fashion blog may not have as broad an audience as the editor-in-chief but could be interested for content creation purposes. Lastly, the advertising chief of a celebrity gossip magazine focuses on sales and advertising, not necessarily editorial content regarding fashion trends.