First of all,
THIS link should be cheaper.
Tell her...
"But the stopwatch will break from me dropping my cube on it when I'm done since I can't click the button AND click it to stop it right when I'm done with my solve."
Or, make a Rubik's Bomb, where you get like a container, cut a whole on the top and put a little timer under it, make as trigger, so you can just press a big fat button to start and stop the timer..