It’s certainly more than urban legend. There’s a Wikipedia article (CG apparently doesn’t like direct links, so search for Logic Bomb) that lists several successes and attempts.
Taking the binders (Presumably company property, as they were produced while employed, for the benefit of the company) is potentially actionable. At the very least it’s a major bridge-burning event, so one may have trouble finding employment in that field again.
Whatever she makes, eat it with a smile and thank her for it.