I agree the porn has to go but it is normal its exploring your
body and that's ok
She's exploring and she has found pleasure from self gratification. Humping a pillow is a form of masturbating. Masturbation is NORMAL at any age especially the preteen and teen period. During the preteen years and some of the early teen years physical gratification is the norm. As the teen grows older, in the latter teen years, there are emotional aspects that latch on and then an emotional fulfillment is as important as the physical gratification.
Everyone fails to realise how our biology works. We need to understand basics.
Your 11yr old humping her pillow naked is perfectly fine. Just accept it and leave her alone. It is very pleasurable and not harmful. Let her explore and experiment. Regarding watching porn, all kids do that these days.
I understand this 11yr old girl because I was in a very similar situation. 4 months before my 13th birthday I lost my virginity to a much older guy who I had a very intense sexual relationship for close to 2 years. I don't regret it. It gave me confidence, I grew up fast and he was the best influence on me.
I'm a doctor for kids and I say it's very normal for boys or girls to be doing that most of the kids that I see have cumed or pillow humped and that is a healthy sign if she's cumming and the porn part is also very normal kids that are going through changes look at that stuff a lot I say let it slide just that one time and confront her that. That stuff is inappropriate and should not do it again or you can say do it in your room only and set limits on it like good behavior leads to 20minutes of playing with yourself again it's very normal