The fact that she let her kid play GTA IV in the first place speaks volumes. I'm really not surprised that if she is such a bad parent that she lets her kid play a game she so strongly disapproves of, that she is also such a poor parent that she has to call the cops to handle a misbehaving child. Of course its also possible that the kid has behavioral problems, but in that case, DON'T BUY THE KID THE GAME IN THE FIRST PLACE! Come on. The games name is a felony. If you can't figure out that this is something inappropriate for children, then you should not be having kids.
This is why I am a huge fan of that site linked a while ago, Common Sense Media. Sure, sometimes they have no idea what there talking about as gamers, they do make it a bit obvious that the writers don't go home and play a round of Modern Warfare, but they certainly have a mission statement of being a comprehensive, unbiased evaluation tool for informing parents on how to help there kids have a positive, appropriate experience with video games. Really, if Common Sense Media became a household name, every parent would have to STFU about video games being evil.