But one could say prepare (say the chant of, but not release the spell) a fireball spell with arcane, then use black magic to create, say oil or some form of flammable gas near/around a target location, then release the fireball.

I'd figure as long as you don't [i]actually[/i] mix the two magic types in the same spell it'd be fine, yeah?[hr]
Noted in regards to the exponential bit. I am leaning more towards her just not respecting authority and hierarchy much unless it suits her...for a time.