I want to "ruin" my girlfriends video game
What makes you want to ruin your girlfriend's video game?
I want to prevent her from playing the video game again
Don't ruin the game for her. She will be mad at you and it can damage the relationship.
It's only a video game, right? I'll get her new video games she can play..
Just don't ruin anything of hers at all. There is no reason to do it, and it can only end badly.