Mal of course is giving excellent advice. The first time that I saw this done, it was done in an ashtray in the living room of a freind, whom I thought was nuts. A very small fire with interesting colors burned, and when it was all burned, there was no fire. The end. What a let-down!
Explain to her that powders BURN, not detonate.
Gasoline is far more dangerous, and she likely thinks nothing of strapping 20 gallons of that to her back every time she fires up a car, or of putting a can in the garage.
Then find something quick (quickly, now!) for her to be right about. ( ! )
L.P.