If you made her right-wing, like The Comedian or a sort of superpowered Margaret Thatcher, you could call her
Lavatory Girl!
I’m sorry, I’ll stop now.
How bout Barbie-Cutie?
Burning Bush
No politics! :D:D:D:D:D:D
SORRY!
Sizzeleen
Well, here’s my suggestions:
Hellfire
Ebony Flame
the Dark Lady (in case you don’t feel the need to stick with a spefically flame-related codename.)
Blackstar
Cinder
Burnadette.