Friend Is Former Meth User?

My friend (who comes from a background of family drug abuse) recently told me she had been using meth on and off for 6 months or so and was planning on quitting. She decided to quit (cold turkey) 2 weeks ago and has said she has no interest in ever touching the sh*t again. She seems to be doing really well – her physical appearance has improved and she tells me every day that she just feels better.

I believe that she is sober now, but am concerned about the reality of relapse. Other than offer my mental/emotional support what can I do to help her? Do all users require professional treatment to REALLY quit using?