Discovered I have a 4 year old daughter who was abused?

Right now Im 25 and a few years ago I was, to say the least, out of control. I was into drugs and I had a lot of flings with different women. In the last 3 years Ive been completely clean and I got my life back in order. However a few months ago one of my exes showed up at my place. She had a little 4 year old girl and she said she was mine. I could tell that she was still pretty messed up and I didn’t believe her that the kid was mine, but at the same time I felt really bad for the little girl and tried to get her and her mom to come inside. I was going to call the police because the little girl didn’t look like she was being taken care of and her mom was definitely on something when she showed up. I went to go get the little girl some water and when I came back the mom was gone and she had left her little girl. I called the police but I went to the police station with the little girl because they wanted to take my statement . I asked about the girl and started to wonder if she really was mine. We took a dna test and it turned out she’s my daughter. I feel so guilty that I didn’t know about this sooner. Her name is Maya and she’s so sweet even though she’s been through a lot of bad things. I recently won custody of her and now she lives with me. I tried to get her mom help but shes disappeared and no one has heard from her in months. Even though Maya is sweat and I love her very much I can tell that she’s very scared by all of this. She seems to trust me but she’s very nervous around people. She has scars on her back and im so appalled that no one took her away from her mother sooner and that no one realized that she was being abused. At the same fault I know that its my fault she was even in that situation to begin with and I hate myself for that. I want her to feel comfortable and happy and she is at times but she just gets so scared so easily. What can I do to help her adjust to all that is happening easier?