Is it normal that my niece's hand is down her pants most of the time?

My niece came to live with me this summer because she had issues living with my sister. I noticed when she is sitting quietly either reading/studying or watching TV she puts her hand down the front of her pants. Not between her legs, but just down the front of her pants.

I've explained that type of behaviour needs to be private. She says it's not a sexual thing, it just feels comfortable. It makes me uncomfortable.