Snap like a promise - Tradução em português

Context: There is an alien having the whip hand over a girl, and it's almost killing her, it warns everyone around them that if anyone move she will die. I understood the idea of snapping like a promise, it's like she will disappear, but is there any expression in our language that expresses the same fun and almost exact idea? I can't think of one.

One wrong move and she snaps like a promise.