Funny/Awkward situation

So my boyfriends daughter is 6 years old. I’ve been noticing that she will get her personal blanket, put it between her legs and basically “rub or hump” the blanket. I always ask her “what are you doing?” And she kind of gets defensive like “nothing??” I’m wondering if anyone has went through this with their own daughters. I’m thinking she’s getting a pleasure out of it, and I’m not sure if something like this is normal?? I caught her REALLY into it today, so I asked her again what are you doing? And she like hopped up and said I’m laying down?? So I said does that feel good or something? And she says yeah... so I said show me where it feels good.. and she pointed to her knee so I know she’s lying. Lol it’s such a funny/awkward situation. So just let me know if anyone has been through something like this!