First Counsellor, she worked at the Italian Embassy in Brussels, then detached, on a special assignment, to the NATO[1] media task-force during the conflict in Kosovo (1997–2000) and appointed at the Permanent Mission of Italy to the UN in New York in 2000.

In 2007 she became Head of the Mediterranean, the Middle East and Balkans Department for Development Cooperation at the Ministry of Foreign Affairs in Rome.

From 2014 to 2016 she served as Permanent Representative of Italy to the North Atlantic Treaty Organization NATO in Brussels, becoming the first woman to hold this position.

On March 12, 2021, Zappia was appointed Ambassador of Italy to the United States in Washington, D.C., by Italian prime minister Draghi.

In June 2019 she was awarded with the "Mela d’Oro" (Golden Apple), a recognition assigned by the "Fondazione Marisa Bellisario" to women who stand out for their contribution, at the national and international level, in public institutions, management, science, economy, culture, media and sport.