When writing to, referring to or directly addressing a female ambassador, speakers or writers should extend the same type of title that male ambassadors receive. However, depending on the occasion, you should speak or write it differently. This goes for communications including letter salutations, event invitations and greetings in person. According to the United States Department of State, ambassadors are technically officers. Note that the United States does not use the title "Excellency" for ambassadors as some other countries do, according to ediplomat.com.
Refer to a female ambassador as "The Honorable" on a mailing. For example, "The Honorable Charlene Johnson."
Call the ambassador "Madam Ambassador" in a letter or invitation. For example, "Dear Madam Ambassador."
Address a female ambassador in person using the title in Step 2 or by adding her last name to the word "ambassador." For example, "Hello, Ambassador Jackson," or "Good evening, Madam Ambassador."
Ediplomat.com recommends addressing an ambassador with their title whenever you are in public, even if you know them on a personal level.