I find that people relax and look good when you make them feel good. In front of a camera, most people become unsure of how they look and that makes them stiff and nervous.
That's why learning to pose people is not a hinderance, it's a great help. If you say, "Just pose naturally," heck they don't know what that is. They've never thought about it, and once you make them try to think about it, they stiffen up.
So you need to have observed human behavior closely enough to know what looks natural and good to the camera and put them into it. That does two things: It assures them that at least one of them (you, the expert) knows what he's doing, and that assurance allows them to relax and achieve a truly natural pose.
Second, if you're going to photograph people as portraits to please the subject, you have to learn to see what looks good about them and emphasize those features--that's your job. Then, when they look good, tell them they look good while you're shooting. Never give them the impression they're screwing up. This isn't baseless flattery--you should be complimenting them on the good aspects that you're focusing on.
If she has nice eyes, tell her she has nice eyes...don't mutter about her big nose, you're working around that without telling her. She'll then give you more out of those eyes. And if she ever gives you an especially nice expression or pose, be sure to whoop it up: "Whoa, what you did right then was great! Do that again!"
You'll find in short order that when you know what looks good, make them look good, and tell them they look good, they'll give you what you want.