N.A.
That is something normal- or so I've heard! I have a friend thats in her 60's and her daughter is my age, but she use to tell me about how her daughter would do that and sometimes even start "humping" the floor,bed, etc! I asked her what did she do about it and she said nothing, but she also said that when she would ignore her that she eventually stopped. I have never experienced this with my kid's but it's not an unusual thing to hear about. She'll grow out of it! Good luck!