Can you pick a nickname that best suits my character?

I'm writing a fan fic about a girl who works for Department 19.

Name: Fallyn Azrael Bishop
Age:17
Height: 5'7
Eye color: Left: Red Right: Grey
Hair color: Raven black
Nationality: Italian/ British


Description: She is an elite member for Department 19. She's worked for them for 5 years, starting off as a weapons tech and made her way up to elite soldier. She's very hostile and quiet. She'll only say a limited amount of words and she likes to get to the point. Her position in the department is quite simple. Eliminate vampires and supernatural creatures.(She's willing to turn on her own kind for what that had done to her little adopted sister, Hannah). She is also a hybrid. Her father is a Vampire and her mother is a Demon, who was killed by the father. She works with her Alaskan Malamute/ Wolf hybrid, Perseus. She is one of the deadliest killers that the department has but she's not used to working with a team. Not many people in the Department know of her real identity.

I have a list of codenames but I can't decide which one fits her:

Raven
Nemesis
Shiva
Inferno
Reaper
Eclipse
Nike
Night Wolf
I would give her an ironic nickname like Angel, or something. It works with the Bishop last name, and it would shock people. No one would know to be scared when they hear "here comes angel" which would give her a major advantage.
Shiva. It's the least predictable and most interesting. That or Nike, but I think most people think of the sports outfitters rather than the Greek myth or the Winged Victory.
Also, was your question also asking for a nickname? Or just a codename? For a nickname, I'd give her a name that humanizes her a little bit more. Maybe "Fay" or "Fally"
A more regular nickname will give her more character ad make her a more layered and interesting character.
Tag: Can you pick a nickname that best suits my character?