Sprite said it all, shes just a normal little girl, its natural and she curious about her body.
It is very normal. If she does it excessively, though she could be having problems such as anxiety, or is stress about something. My ten year old granddaughter came to live with me and had odor on her hands a lot of the time. I worried at first that someone had done something to her, but realized it was from losing her Mother (my daughter) and having to go live with her unfit father. Moving again was yet another loss in her life. I did NOT scold. I just asked her to go and wash her hands as they did not smell very good. I told her that I knew what she was doing and that it was important to keep her hands clean. Because I accepted it, I have observed her stopping or at least lessening her masterbating. NEVER scold. It is very natural. Even grown ups do it at times. It releases tension and feels good.