A derby girl is personal matter. It needs to reflect the empowered you. All you are, your likes and dislikes, your culture, your personality to shape the name. It's should be a name you feel proud wearing out on your sleeve for all the world to see-- this name is your armor, your derby personae-- and when you wear it proudly nothing can touch you. but still be okay dropping it once you're out of that ring.
Here read this. It should help you generate some names and when in doubt you could always bounce some names off me.
I'm still tinkering with mine but Miss Murder, Sudden Death, or Miss Fortune all have a nice ring to them.