She became the American 'ambassador to' Italy [=she began representing America in Italy] several years ago.
a 'goodwill ambassador' [=a person who travels to different places to promote friendship and goodwill]
an 'ambassador' of hope [=a person who tries to bring hope to another country or group of people]
(..) The man who came to me the other day about burying his father. Hizdahr zo Loraq? He will accompany the Second Sons and serve as my ambassador to Yunkai. He will tell the masters what has happened in Meereen. He will explain the choice they have before them. (..)2014 TvShow: Game of Thrones Title: Mockingbird Season: 4 Episode 7