There is some merit to this, doctors - at least of the kind described, YMMV depending on where you live and what doctor you go to - certainly aren't interested in finding these kinds of causes, but be aware that things can go too far in the other direction too. To take a rather extreme example, if you take this approach too far, especially confrontationally, to someone who is seriously depressed, you may very well be the straw that breaks the camels back, and they end up killing themself instead.

Regarding the article in question, there are plenty physical ailments that show up as fatigue etc. and are not helped by sleep, food and exercise, but should of course not just be masked by pills either. OP seems to take it for granted that the girlfriends problems are the result of something she's doing or not doing. That may be the case, but it might also not be. Doctor should investigate these possibilities too.