Let me get this straigh, your friend is only 17 years old and is still in high school. If you do not feel like telling her parents will work is there a consuler at school you can talk to. Your friend is an addict and she need major help, but if she is not willing to see that she has a problem there is nothing you can do for her.
I would tell some adult what is going on, with her. If she is thinking about doing it she will do it. You said you will not go thur losing another friend. You will if she uses crack.
I understand you guys are in high school and think you can handle anything. You are very good friend, and u know u have to do whatever you need to.
Try maybe going to a rehab place and see if there is not someone there that can help your friend out. Maybe if she sees what happens to long use of the drug or short use of the drug will do to her. See seems to be one that may have to see with her own eyes what happens to a crack user.