Yes, people have been able to quit things like meth, fent, heroin etc with the help of psychedelics, DMT included. I don't know what you read and where, but in this case, this individual you are asking on behalf of might have all sorts of medical complications resulting from prolonged abuse of "hard" drugs. These complications might include an exceptionally weak heart.
Profoundly intense experiences like those often induced by DMT might not be suitable for people with cardiac problems. And that's just one problem that might arise from abuse of meth and fent. Nobody is saying DMT is as dangerous as those two. What I'm trying to convey is that introducing a powerful, exceptionally intense substance into the mind of someone that might already be severely weakened by substance abuse, might produce the opposite effect of what you're hoping for.
There's no need to be arrogant and passive-aggressive. Again, if you're waiting for someone to greenlight your salvation plan and say "yes, let your pregnant obese addict friend consume one of the most intense substances known to man and hope things go well", you came to the wrong place. This might be a matter of life and death, and as such, the Nexus will not play the role of arbiter for what I consider quite obvious reasons that have absolutely nothing to do with courage.