Which is pretty much what you have to do when one of your characters starts doing it, unexpectedly. . . and there's a limit to how far you can cut her talking down because it will determine her next actions.
The rules of magic will determine a whole heck of a lot about what the character can do in a setting. Is the magic inherent in inanimate objects like gemstones? Is it found in living beings, but only unintelligent ones like gryphons -- or moly? Or inherent in some non-human characters? Or, for that matter, human ones -- I don't like the trope where magic is the provence of some Special Little Snowflakes, but it's clear I'm in the minority, or at least a lot of people can stomach it. Does it have to be learned?
If it has to be learned, beyond the questions of incantation and sigils and whatnot, there are the principles it works on. Elemental magic? (European four elements or Chinese five?) Similarity and contagion? Will power? I suspect my heroine is going to shortly be philosophizing about how there is no such thing as darkness, any more than there is silence or cold, all of those things being absences rather than presences.
As a consequence, she and my hero get to make a big castle fall down. One does, after all, have to use it as a plot device to justify it. 0:)