Serious Issue - What do I do?

My SIL is 36 and a 15+ year meth addict and alcoholic. She’s violent when intoxicated and has had one of her children taken away from her. The drugs have seriously affected her mental health. She’s horribly schizophrenic and has serious lack of common sense. She has never had her own place and drags her child from place to place staying with friends or family. The child that she does have is from a man that was never in the picture. She’s 3. She’s been arrested in the middle of the night while with her child for being intoxicated and getting into a fist fight at a party (yes she took 10 month old to a party and got black out drunk). She’s always been promiscuous. That little girl has been through so much shit in the past 3 years. But more recently, she’s been vocal about the different men her mother has sex with in front of her. My SIL told my MIL it’s her business if she wants to have sex in front of her child. The child will recount what happened and state that she cries on the floor scared during it and her mom won’t pay attention to her. She won’t put underwear on her child, she lets her run around the neighborhood back and forth from neighbors houses unsupervised and even if she’s in a dress will not put underwear on her. She won’t wipe her when she goes #2 so the child jumps off the toilet and runs around when she’s done going. She gets frequent UTI’s, she has high blood pressure (at 3 years old!) and severe sleep apnea (she’s overweight - she wears a girls size 6 and she’s just turned 3). She barricades her bedroom door so the child won’t get out of the room so she can sleep until late afternoon since she’s up until 4 am high on meth - she keeps the child up until 3 am too and says theres nothing wrong with it - then the child will get spanked and yelled at for pooping her pants while being trapped in the room because according to my SIL she needs to wake her up so she can go to the bathroom and the child does but her mother sleeps like a rock when shes been high and she can’t wake her so she’s stuck. She displays acts of sexual nature like poking others in the vagina or saying it burns when someone puts their finger in your butt. I’ve actually witnessed a nasty tear at the opening of her vagina which I was told was from a yeast infection she had. Her mom forces her to breastfeed even though she never had milk to begin with but at 3 years old she’ll make her try to the point where the child cries and fights and asks for a bottle. Her mother can only keep a job for about two weeks then quits or gets fired. The family has alerted CPS and the police and they did nothing. The social worker checks in on her but she puts on an amazing normal front and acts like she’s the victim and calls her daughter a liar to discredit what she says. I’m really alarmed that her social worker hasn’t picked up on her mental health issues because no one can carry a normal conversation with her but CPS is swamped with work. It’s extremely painful to watch and I am at the point where I want nothing to do with them because I can’t handle letting this happen and no one else around me thinks any of it is a big deal. No one cares but me. At the same time, I don’t want to abandon her because I’m the only decent person in her life. I went to college, I have a home, I make six figures (not to brag at all just for comparison purposes) and I have a healthy environment for my own children. We’re “normal” I guess. I wish she was born to someone else. Even my MIL says she’d be better off in foster care than with her own mother. What do I do? I can’t watch this anymore. It’s nauseating and I lose so much sleep over worrying about her. My SIL’s irresponsible and out of control life is driving me to worry for the child’s life. She’s on more than one occasion driven drunk with the child who is in a booster seat (not even the right car seat for her age) she has been dragging her child on the bus making her walk so that her doll can be pushed in the stroller for the past couple of years and she just bought a car. I worry every night that she may not make it to see her 5th birthday but since there’s no physical harm and no “immediate danger” CPS doesn’t give a shit. What would you do? I’m ready to just say I want nothing to do with my SIL and don’t wanna see or hear anything that she does anymore. Mind you she keeps saying she wants 9 kids! I’m honestly hoping she gets pulled over drunk so she can go to jail again and let someone else take the child. I’m going crazy, I’ve been going through this since she was born. The stories are endless and even cries for help got her nowhere. I’m lost.