The only reason I can think of is that she saw the opportunity to try and embarrass that smug git on live TV, like he has done to the countless hundreds of people who have auditioned on his money making shows over the last 10 tears.

I'm only surprised that no one has managed to get a gun into one of the American auditions and increase the IQ of the planet by a few points

Well she has achieved more publicity for BGT.
I am not totally convinced anything to do with Simon Cowell isn't staged.
In this case probably not, but I've always got a small doubt.

After reading part of their blog experience on BGT (which is very witty and droll), I have now changed my mind on the staged theory.