Custody Change in Case of a Minor

In the case of a seventeen-year-old girl who will be attending college in less than two months, does she have a say in the house in which she will live for the remaining months? If a mother is mentally ill with bipolar disorder and the step-father is no better, what would the girl have to do to live with a grandparent (the grandparent has already agreed if it possible)?

Technically a 17 year old is still a minor and cannot chose where she will live, however if the child, on her own accord comes to stay with you, you would not be in violation of any law by providing her shelter.