Yes. There is a system that prevents people on the same IP (that would be your gf) from interacting with each other. It's a hard block, so if my wife and I are both playing, and I attack province x, she can't attack province x for 24 hours. So what that means is if you're both attackers, you can't hit the same target.
There are some additional heuristic checks we do beyond that to identify multis as well, so don't log each others accounts :).