She's a teenager.

She's actually SUPOSSED to be going through different looks and phases; that's how you start to find your own identity away from your parents/the adults in your life.

I see nothing wrong with what she (or Miley) is doing. If anything, I'm envious that they feel so free to look how/do what they want. I wish I had been as brave when I was a teen (hell, I was I was brave now).