To update all...
On friday after i picked her up she told me she wanted to live with me now. I have been preparing for this for a while really, and have been aware of the stuff scully mentioned: (thanks scully for putting it very neatly)
To answer your question though, prepare to have her move in with you. Clearly she does not want to abide by JW rules, and her mum and step-father want to shove those rules down her throat. Have a sit down with her prior to her moving in and make it abundantly clear that while you are far more liberal than her mum and step-father, you are concerned about her safety and, as jamiebowers said, will not tolerate drug or alcohol abuse, you expect her to be responsible for her overall well-being (eating disorders) and particularly so when she is sexually active (birth control) and she has to take school seriously. Set curfews for her, give her chores and an allowance, and once she's old enough to get a job, she should get one.
and yes, i see kicking out reserved for real rebellion with stuff such as drugs etc.
At her request i called her mother and told her the news then passed the phone to daughter to speak with her mum. It was a difficult call to make and left my daughter and her mother in tears. She will miss her little brother and sister very much and her mother asked to not be a stranger and can visit anytime. So thats a pretty good outcome. There are a few behind the scenes converataions that took place over the last month, thing both her mother and step father d=said that led to the move.
I look forward to being a full time dad and will do my best to keep steering her in life. Stay tuned...
thankyou all who commented on what is a challenging situation