I am sorry but, it is not as simple as locking her up somehwere for 2 weeks and she will be cured. My sister has had problems on and off with drugs for years. She has gotten away from it several times but, always seems to slide back. It is more than just the drugs, it is the people she is hanging around with. The drugs don't always come first and then the bad crowd, the bad crowd generally comes first and then the drugs. It could also be an emotional issue and she is using drugs to cope with it
If she is 17 like you Steve than her parents/family need to be involved. Let them know, this is something for her family to handle. I know it is hard but, there is little you can do but try and be there if she needs you.