What to do in this situation?

So last game I had a caitlyn on the other team go 2 5 then quit the game. And by quit I dont mean exited, she stayed in their base dancing until the game ended. How do we report something like this? The system shows she stayed for the whole game, but she completely ruined the game for the other 9 of us. I love winning games but it means nothing to me if it became a stomp because of one person doing something like this. So my question is, how do we get someone like this punished?