This is a cool trick

Homeostasis would kick in and (if you somehow managed to override the autopilot in your brain that would probably force you to breath) you would pass out. Without your conscious control of your breathing the stop you from gathering oxygen, that autopilot in your brain would force you to breath, saving your life.

How would she know that works?

My uncle was a fireman and some guys from his crew could hold his breath for 7 minutes.

Only if it was that easy