Whilst I'm not gonna say that she was using a 3rd party charger (I would rather stick to facts than speculation) - I just thought I'd share my experience of one. I bought a cheap charger off eBay a couple of years ago.
It worked great, then one day I plugged it into the wall, and the other end into my iPod and *bang* - the charger exploded, it shot the charger out of the wall and across the room, charring the wall and blowing the circuit breakers.
Luckily there was no fire and no one was hurt, and the iPod was ok (somehow!) but I couldn't help but think that I was lucky and I could have received one nasty shock from that thing.
I now buy all official chargers every time, it's just not worth it for the sake of a few pounds.