Well at least we learned something today: Make sure you keep all of your receipts...
I had an old mp3 player that did the same thing, it would only play on only one side of the the earphone. I found out that if twirl the earphone plug just a little bit it would play on both sides... weird huh?
The thing is that sometimes there's not very good contact between the head jack and the earphone plug.
Tell her to be a good girl and you'd buy her a new one...
