Child Abuse: Helping a Child the System Failed

My question involves child abuse or neglect in the State of: Tennessee. I'm the mother of a 16 year old boy who's 17 year old girlfriend had been sexually abused by bother her real dad and stepdad. Sexual abuse stopped 2 years ago after stepdad had a daughter with her mother and she was no longer willing to allow it. Once she started seeing my son stepdad was jealous and protective and verbally aggressive to my son but not in a fatherly way more like jealous boyfriend. Dcs started an investigation last week and interviewed the victim, then Monday her 2 siblings, finally yesterday her mother. Dcs made stepdad leave the home during the investigation. Mom drove him to his parents house and has been going daily to see him and helping with utilities and groceries at her in laws house and obviously doesn't believe her daughter. She has accused her of destroying her life and tearing the family apart. Mom works a 3rd shift job as does stepdad at the same location so the victim is forced to basically raise her 3 younger siblings,cook,clean,she isn't allowed to friends houses or to the movies normal teenage stuff nor is allowed company. She is a prisoner and slave in her own home enduring physical,and emotional abuse and dealing with the past trauma of the sexual abuse on her own. I was informed this morning her mother told her I have papers dcs gave me giving me permission to allow stepdad back in the home whenever we see fit and telling her see I told u that you wouldn't get your way and if you run away I'll have u locked up and there's a chance I might send u out of state with other family. The dcs didn't believe her I guess given she was the only one in the home sexually abused and it happened behind closed doors without witnesses and mom coached the other 2 kids on what they were and we're not allowed to say so they didn't get all the facts, the physical and emotional abuse was never mentioned. She's scared and will be in imminent danger when he returns to the home. She's just turned 17 in the middle of January so still another 10 months til she's legally an adult. I'm willing to give her a place to stay here in my home but I'm her boyfriends mother..how can I help this girl?

Child Abuse: Helping a Child the System Failed