Kerridwen, after the Celtic Goddess of Fire, Poetry & Prophesy.
That sounds like something your dentist would treat you for.
Therma
Branda
Miss Flammable
Burning Girl
White Heat
Volatile
Igna
Flare
Spark
Fiery Angel
I’m not very good at this, sorry.
A middle-aged heroine with those powers could be Hot Flash. 
Ember
Tinderbox.
Heh…that edges into burlesque comics territory. It has fairly crude double entendre written all over it.
That’s what I was thinking too, but hey, most of the other obvious ones were taken. And I’m a sucker for getting as many layers of meaning into a superhero name as possible.
Hotty McHot-Hot
[Groundskeeper Willie]
Ach, I’m bad at this!
[/GkW]
I doubt I’ll go with that, for fairly obvious reasons, but it appeals to me.
This is why I love the Dope - you get the obscure, the clever, the lewd, and the punny.
I can see June asking her family for suggestions:
June: Uh, yeah, so I’ve got these fire powers now. Well, you saw. I just don’t know what to call myself.
Dad: Corona. Blaze. Scorch…
Sister: Flamage… Massive Flamage.
June: Uh…
Sister: You’d have to pad your bra though.
June: glare
Mom: Gehenna
June: What?
Mom: It’s the Jewish hell.
June: Oh. No.
Dad: Fire queen. Conflagration. Napalm. Salamandra!
Sister: Hot stuff.
June: Stop with the porn names, you perv.
Sister: shrug
Mom: Kerridwen or Belisama.
June: Again, what?
Mom: They’re Celtic goddesses.
June: Why do the Celts have more than one fire goddess?
Mom: Well, they have other things they do too.
Dad: Tinderbox.
June: …
Sister: … snicker
June: DAD!
Zebra’s Love Slave?
Habanero?
Cindrea le Hot
Flashpoint (It fits with the teleportation, too.)
Firebrand
Balefire (Refers to a signal fire or, archaically, to a funeral pyre. Also spelled “baelfire”.)
Firelash
As yet another City of Heroes player, I have trouble remembering what fire-related names are already taken, sometimes.
Sizzle Stick
Creme Brulee
Pro Pain
Bunsenella
Lux
The Kindle Kid
(not sure I’m good at this)
Holly Cost
Charwoman
Pele
My first thought as well, along with “Powderkeg”, but it sounds like they won’t fly.
Of course, since it seems like it’s the “box” part you’re having trouble with, you could always go with simply “Tinder”.
Alright, so far I’m tied between Blaze and Balefire. And still being tempted by Tinderbox and Flashpoint. Despite the connotations. I’ve done worse things to her.
Fireheart or Firestar.
Okay, they’re both names for a cat in a children’s series (same cat, different times in his life) but hey, they work within the parameters.