The most likely scenario is that you have communicated some information to a third party and they have relayed that information to your ex. You could have done it in game when playing or chatting with another player. You could have done it out of game. Unless there is some kind of security loophole at Blizzard (which I highly doubt), your ex has some kind of spyware on your system (like Spectersoft programs), or she is a computer genius, the third party is more likely.
- - - Updated - - -
Some spyware programs do not show up on most scanners. Programs such as Spectersoft software are often omitted, because they are blatantly overt on the install.
And just to be clear, I earn a living as a computer tech. I clean crap like this up all of the time. I am not just talking out of my ass.