trigger warning ⚠️: this discusses suicide attempts, sexual assault and recent mental hospital stays

I came into my stepdaughter's life when she was 11 and a half. Her living arrangements were she lived in another state, 4 hours away from her dad, with her mother who had a long term boyfriend she lived with for the past 8 years. She would come to spend summers with her dad and he would visit her at least once a month in her state for weekend visits. 
Her 11th summer when she got back to her mother's things changed rapidly. 

Mid October of 2017 her mother lost her job due to nodding out at work, as told by her bf at the time. Her bf dumped her due to her cheating on him. Mother moves into an unfit home where her daughter had no room of her own and slept on a couch with the man her mother left her long time bf for. Her mom was beginning to be hooked on meth not that my step daughter realized it at the time. 
One night her mother didn't come home. Texted her dad hours away at midnight saying her mom was supposed to bring her dinner. She's worried. That very next time my now husband goes and gets his daughter and she's been living with him full time ever since. 
The mother has made 2 attempts to come see her daughter where she lives. She has broken promises left and right. She hasn't had a job in almost 4 years. She was arrested 4 times last year due to drug charges and contempt of court. All the while her daughter has spiraled into serious depression and anger out on US. 
My stepdaughter has made 3 solid attempts on her life. Most recently 4/19 where she was released from acute care and 4 hours later overdosed on her prescribed medicine. She has been in acute care waiting for residential placement ever since. She begins Friday , hopefully, where Dbt will be the main focus of therapy since she has done 97 days in residential where CBT treatment did nothing and she has had 6 acute hospital stays over the past few years. 
She exhibits classic marker signs of BPD that I've read about but since under 18 they won't give her that diagnosis fully. Just that she exhibits the attributes. This child is a very abusive girlfriend. She has tried making suicide pacts and has sent lewd photos and videos to just about anyone who asks. We take her cellphone away and she uses that as ammunition on suicide attempts. She tells us she hates us and weaponizes her mental health against us. That's how it feels. I have depression. I have anxiety. I was driven to the brink of a nervous breakdown myself due to all this. My husband is very passive and it's difficult just so difficult. I don't know if my step daughter wants to change. I think she really enjoys the negative attention because it's attention regardless. 
I may not have said things right I apologize. We DID find out she was molested during her care at her mother's and we believe this triggered the personality disorder. She immediately started physically lashing out after that 11th summer. 
I don't know if I can stay married to things that don't seem to change. She has punched walls and pits my husband and I against each other. She rejects discipline. I'm so scared this residential treatment won't work. 
DCS is involved this time around because of the police coming to the 911 call. They've been very kind and helpful. 
They know this isn't our fault.