[la vida loca]

Suppose you approach her mother and the response is a resounding NO and she cuts off further contact with you. What then? You may want to consider whether it is more important to adopt this child or help this child (not that the two are mutually exclusive but you may have to make a hard decision). Are you absolutely sure you can't get child services to intervene? At least then her mother has a chance to set things right with her child by getting help and formulating a plan. If things really are as bad as you describe you may still eventually have the opportunity to adopt her in the future.