Although we have helped and tried to guide some kids beyond our own, we have never done something as significant as what you are doing - so no experience to share. Looks like some knowledgeable people here have covered the legal aspects with suggestions - so I won't try.
But, given her emotional state and the nature of the parents, I would second the advice on good judgment in being with the young lady, particularly alone, because the noted potential is all too real.
You are trying to do the best kind of thing - but avoid being stung for your good works. Once the situation is stabilized - legally and emotionally - your instincts will let you know how to be.
That said, I truly admire what you are trying to achieve with and for this girl, and wish every success for you and your family - and for her. You may very well be saving her from a bleak future and putting her on a path to excellent well-being - and you may be saving her life.
Try to remember that what you are doing, and how well you do it, will quietly speak volumes to your own kids and other folks who know you - in the most positive terms. That is powerful influence on other lives well beyond that of the young lady you are helping. Be calm, thoughtful, loving and strong - praying for your guidance.
