My brother has given the care of my niece to our mother

Being poor and not potty training a special needs child by the time a child without those challenges might have reached that milestone does not a case for neglect make. He might not be the best father, but parents do have a lot of latitude in how they raise their children. That includes hairstyling, bathing, and who they spend time with. If CPS isn't finding cause to remove the child, you are not going to be able to get custody without his agreement. You can enforce the order that exists, but as you have been told in the past, you need to go to court to do that. If you are unwilling to take that step, you are out of options.

OK. I don't get where this is coming from. I never said I wanted custody. I never said I wasn't willing to go to court to enforce the visitation. I am talking about my niece having matted hair, not having "unstyled" hair. I am talking about the child going poop in the front yard, not wetting the bed. My question was what to do about her current living situation. And there are other facts I don't want to publish on the internet. But thanks for your interest.

If you won't give specifics, your only option is to hire an attorney.

I understand. I have already given enough specifics including the dead baby ( born 14 weeks early and cocaine positive). What the public expects from CPS and what they actually do are two different things (at least in my area) and I have said that she has been removed three times in her short life. But I thank you for your interest.

Your standards are higher than the parent and CPS, and reasonably so, but the truth here is that if CPS is not taking further action it is because they lack the legal justification to do so.
Sure the child may be better elsewhere, but that is not justification to take the child from a parent- even a bad parent.
I would assume CPS is offering various resources for help, but they can't make anyone accept that help. If it is as bad as you say hopefully they do regular visits for follow up to monitor the situation.
Short of offering you own assistance (assuming you haven't done so) it seems you have done all you can. Continue to report any suspected abuse. Maybe somewhere along the line they will find something they can work with.