I consulted with some legal folks to verify the issues surrounding running away, and I learned the following:
 
Parents can request a court order to have their child returned to their custody (law enforcement would help to pick up the child and return them home). In some cases, parents may decide that they cannot continue with their parental obligations, and they can request to be "relieved" of their parental obligations, placing the child under the supervisions of the court. Finally, if a child is determined to be "incorrigible", they can be placed in a juvenile detention center. I have heard stories of teens were were threatened with a 10-day stay in a juvenile detention center.
 
If your friend was 18, I would say that the risks are larger for him, but at the age of 17, the consequences are less severe (depends on the parent's actions above).
 
These are the legal issues. The emotional piece of this is how your friend is feeling about her family and life situation, in general. She sounds pretty sad and hopeless. If she has ever felt (or currently feels) as though she does not want to continue to live, she needs to know that there are lots of supportive people out there that can help. She should tell her parents and/or call a local or national hotline to talk about her feelings. We have worked closely with BoysTown (not just for boys), and they are wonderful. Their number is 1-800-448-300 (it's free!). http://www.boystown.org/AboutUs/hotline/Pages/CrisisHotline.aspx. They are available to talk.
 
There are people who care (including her parents) and it is important for her to know that things may seem tough, but they won't always be this difficult, things can be better, and there are people who care. Although it is understandable that she feels like running away is her best option, there are better ways to get the support she needs.
 
Best wishes,
L. Compian, Ph.D.
Child Psychologist
Education.com