Well, as the article I posted above says that there isn't solely a genetic correlation. Environmental factors play a role. She could be more predisposed to it, however it also depends on the person, their life experiences, and perhaps the experience they have with the substance. Again, a car crash or other traumatic event, or series of difficult life experiences can also trigger latent mental disorders.
It's hard to say, I'm not sure whether a psychological evaluation would be of much use either. If this person has suffered persistent delusions, psychosis, extreme mood swings, excessive paranoia, etc, prior to ever taking drugs it would be advisible to say that this person should abstain from them unless they are fully willing to deal with the possible consequences that may occur as a direct result of the use of these substances.