Online interactions are pretty much unrated in these games, the rating only covering the in-game, developer provided content.

As for the topic on hand, I would advise the same as some others. Use this unfortunate "opportunity" to have her learn to handle situations like this, or generally dont let her near online games. Preventative measures dont really exist for this kind of stuff. You can punish the perps afterwards, but by then the "damage" is done.

You can make the consequences for being an a**hole severe, but personally I dont think that being an a**hole warrants greater punishment than a verbal warning. Naturally actual harrasment is another thing, but a salty statement flinging blame for a wipe most certainly doesn't constitute as such.