My foster daughter said if we send her back to her mom she's running away

I've been trying to cheer up my foster daughter. She's 15 and the court is trying to reunite her with her mother. Her mom has done her time in jail(9 months) and completed her classes. My foster daughter was sex trafficked by her mother for drugs from as young as 4 until she was taken away at 13. She has already said she doesn't want to be sent back and I was hoping they would terminate rights and we could adopt her. I legally have to follow whatever the court says and I've tried to fight it. Mom's lawyer is saying she's sober now. She's ready to be a good mom. My foster daughter said she doesn't want to get back. She told me today if I send her back then she will know she has nobody in her life who ever actually cared about her. She's not understanding that this is our of hands. She told me she's running away. She'll live on the streets if it means she never had to go back. I've told all this to the caseworker and the caseworker keeps saying once they're back together and she's with her mom she will change her mind. Nobody is taking me or her seriously and I don't know what to do.