I don't know anything about medicine or statistics. I just want to ask you guys this: How many of those who criticize psychologists or psychiatrists have been treated by one? There are a lot of myths and prejudices regarding them, and I used to adhere to most of them. But if I hadn't seen a team formed by a psychologist and a psychiatrist years ago, I would be dead by now (yeah, I had
a lot of problems in my head

, but most of them are cured now).
These specialist not only gave me medication for a brief period, but also helped me solve my immediate problems and taught me how to deal with them more effectively in the long run. Hell! even to this day I'm still making progress in my OCD, and it's been a lot of time since the days when I was under treatment.
Just my two cents.
By the way, Dilmah G, may I respectfully ask what is exactly the problem your sister has? At least where I live, even people who would be considered "normal" (whatever that means) see psychologists regularly (don't ask me why), so I can't see what could go wrong if you tried.
In my experience, you have to look for a psychologist that your sister feels comfortable with, not just any psychologist.