How kind of you to stick with your friend through this. You are a very good friend indeed and I applaud you. Your post struck a chord with me because I know of someone who kicked heroine only to become depressed to the point of suicide. Despite the depression, the suicide was unexpected and the world was deprived of someone very special. I would so hate this to happen to your friend, not the least because she probably has a whole heap of untapped potential.
Typical of depression is this insistence by the sufferer that they're perfectly happy with their situation. As Ummmm says, maybe her confidence has been knocked and this is her way of pretending otherwise, to the point where she convinces herself she's OK. You know better, of course, and so will she, in the end, but right now she won't thank you for your help. Please try to accept that this is the nature of depression.
Have a look at
http://www.talktofrank.com , maybe even give them a call. They should be able to give you ways of helping.