In care of an 8yo

I had been here in recent history. Me and my fiance currently taking take of my 8yo god daughter. Her mother has had three episodes of mental health issues. The last boute we had her daughter for over a month with little concern from mom. Now recently she's escalated to trying to take her own life.

Some more back story on mom. Shes a single mother. She is very autistic with some PTSD and more. She works but barely makes ends meet. She has a bad habit of having too many animals and not taking care of her home. There has been several occasions where her house is covered in garbage and animal poop and pee.

Her daughter is behind in many ways. (In my opinion.) For example we have to teach her how to bath and how to use the bathroom.

I'm frustrated at this point. I want custody of this little girl. I'm tired of putting this little girl throught this emotional distress. We have not called DCFS as we are afraid of her being pulled into the system. We got mom resources last time to help her. We cleaned her apartment. We bought her daughter a whole new set of clothes as she came to us with nothing that didn't smell like pee. I have started looking into thearpy and other resources for her.

My main question is, in illinois what is the best way to get custody of this little girl with the least amount of trauma. Thank you everyone in advance.