Before the Takeover
Ambassador Castillo originates from a city in Mexico called Xipica, which she describes as being around the same size as Boston. According to Castillo, there have been no living children born in Xipica for six years prior to her diplomatic mission.
In the Present
"A Woman's Place"
Castillo leads a delegation of Mexican diplomats and trade officials in an official visit to the Republic of Gilead, in an effort to create partnerships in trade and see the effects of the Gilead cultural movement. At an initial welcoming party in the home of Commander Fred Waterford, Castillo questions June Osborne about her experience in Gilead, particularly whether or not she chose to be a Handmaid. With great self-control, June tells the delegation that she has "found happiness" in her position. Castillo also questions some of the Wives about their perspectives on Gilead, and reveals that she has read Serena Joy's book and saw her previously during a speaking engagement.
Later, the Handmaids are then taken to a party that serves to both honor Gilead and show the foreign delegates their success, including presenting the children of Gilead. Castillo appears overjoyed at the sight of the children. Alma remarks to June that the delegates are interested in fertile women as a commodity to be traded between the two nations. The next day, as the delegates are leaving, June tells Castillo and her assistant Mr. Flores the brutal truth about Gilead. The Handmaid pleads for their help, but Castillo claims that she cannot help June and explains her own country's dire situation with regards to a lack of children.
After Castillo leaves, Flores reveals to June that he knows her husband Luke Bankole is alive and he may be able to get a message to him, which implies (and later confirms) that at least some elements of the Mexican delegation have contact with the refugee community in Toronto and the remnant U.S government. However, it is left unclear whether or not Castillo herself is involved with this contact.