The villainous (and deceased) Dr. Emma Miller
Dr. Emma Miller was a villainess from "Krewe," episode 3.21 of NCIS: New Orleans (airdate April 18, 2017). She was a physician for Doctors Without Borders, and was a member of the Bancroft Family Foundation of New Orleans.
Emma was close friends with Nadine Bancroft and Josephine Bellacroix, and a few years prior to the episode's events, Emma and Nadine visited Bellacroix during her military tour in Sudan. The women worked on building a girls' school in Khartoum, only for the Boko Haram terrorist group to attack the village and its people. The trio of women bore witness to the group's horrendous actions, leading to Emma agreeing to collude with her friends to steal guns to send to the villagers.
The trio took the guns from Nadine's father's weapons company, and they were all shown (disguised) in the beginning of episode stealing the guns from a train. They were confronted by local police, leading to a shootout between both sides, with the women firing rubber bullets at the officers, as their intent was not to harm anyone. During the shootout, Bellacroix was shot by one of the police officers, with Emma tending to her wound.
Emma's reveal began after Bellacroix was found shot to death in her home, as it was revealed that the rubber bullets were from the Bancroft company. It was at that moment that Sebastian Lund pulled Emma's file after she was revealed as a friend of Bellacroix, and after this, NCIS headed to the Bancrofts' charity event to find Emma. Emma was found behind the fountains shot to death, and it was after this that Emma's villainous role was revealed, along with the revelation that she (like Bellacroix) was killed by Boko Haram.