Biggest advice, find a way where she could not read of the website. It ain't a good impression for a young girl to read, she could develop a porn addiction and cause some harm towards her education. More or less, try to express your concerns with parents and tell them to block the site, there's child block for a reason.
This is very, VERY bad in so many levels at this age. You need to tell her parents asap to do smt about it, having access to adult content (let alone a content full of rape/abuse) at this age is brutal and traumatic and it won't take long for her to end up in some REALLY f*cked up situation out of curiosity and naivety... Oh my god please protect this child, seriously, if this keeps going, a tragedy will be just around the corner.
I saw her when we visited their house and I was sitting beside her and I saw reading it and I said " what is that" and she leaves her chrome very quick and opened tiktok and act like nothing happens (⊙…⊙ )