Neice neglecting her baby

OK you guys I need help, my neice is serverly miss treating her 17 week old baby, they live in a filthy house and the baby is so dirty! :( she has inground dirt on her head, eyebrows, under her neck and her hands, she's so skinny her spine was digging into my arm when I was holding her, I've tired to tell her she needs to stop neglecting her but she said there is nothing wrong with her, it's the worst part because she can't see what's wrong, what do I do? I have pictures of her in the state she is in, if you want to see I can message you them. What should I do?