That'd take some serious patience.  Indigo is the most proficient magician in the guild, and she's not planning on using any other spells for the duration of the event.  Simply keeping the tornado going doesn't take as much magic as getting it started (after all, fires started by magic don't require the pyromancer to keep feeding the fires to make sure they don't go out) so she can go for hours.  Not much more than that, but still.