Adopting a teenage family friend

Hi everyone, as the title states, my wife and I are looking into adopting a family friend. Well that description is odd and vague. She is seventeen currently living in Kentucky with her birth father. We met her through some friends. Her sister is daughter to our friend but they share different fathers. Her father has cared for her very little. Has done nothing for her education, she has not attended school since the 7th grade. At seventeen she is able to move out in Kentucky and her father and stepmother have told her to do so. My wife and I are very close to her and have already told her we would take her in. The three of us have discussed adoption but I honestly do not know where to begin. We don't have children and can't have our own. I want to give her a loving home and parents who actually care. Her mother is just as inactive in her life as her father. Any advice would be appreciated.