She got gall bladder surgery, a specific diet tailored to her actual body, and meditation lessons. All of this helped her health in general--not to mention started her being able to lose weight for the first time--a lot more than just being told that she lacked willpower.

This! I think it's super-useful to keep in mind that even if weight is the main problem, losing weight can be a major, complex process, which works differently for different people.

One of the most effective things I've seen was a nutritionist who worked by meeting with her clients every week, discussing what they ate and when and how they felt about it and what they were thinking about when they did. And what exercise they did and when and how they felt about it and what they were thinking about. And I believe that she worked on the principle (and tiamat360 pointed this out in conversation yesterday, and I think it's vital) that lifestyle changes were changes, real and permanent-- this was not "going on a diet" which the clients would then go off again later, this was actually making a significant and permanent decision about how they lived. And that requires much more thought than just telling people, "okay, eat less and exercise."