Here is a question for parents...?

I have a friend who has a child she loves dearly. She's an only child and my friend is a single parent. Here is the problem. My friend's daughter has been acting up A LOT. She has tried many different forms of punishment and she asked me (because I'm good with children) why it's not working. Her daughter just gets more and more angry and yet punishment is the only thing she tries. Why can't she get that punishment is ineffective and obviously there's something deeper going on here?