What should I do in this situation?

My friend has a major drug & alcohol problem. She drinks, smokes marijuana, heroin, meths, and does cocaine. Pretty much any drug she can get her hands on. She has been in rehab 2 times already. It has not changed her one bit. She gets out and is clean for a month then starts doing the drugs again. She is on a 10 year backup because of a felony she got over a year ago. She has to check in with her probation officer once a month. Well she knew she was going to test dirty so she turned herself in. She only did it to save herself from going to prison for 10 years. Now she has to go back to rehab on the 24th of this month. I really don't know how long she will be in rehab. But I really don't think it will do her any good. She will just play the system get out and be right back on drugs within a month. Her probation officer has already sent her to jail two times in the past 10 years. I dread her going back to jail but feel I have done all I can. What else can I do to get her off this path of self destruction?