I think your friend is going to have to add regular exercise to her weight loss plan - if she can find a way to include weight training in the plan (to build muscle), that should help a lot.
One of the problems with long term dieting (without exercise) is that it lowers metabolism. Your body adjusts to the lower number of calories and thus when you stop dieting and go back to more normal eating, you quickly gain weight. It's like your body is saying: "Starve me, and I'll just learn to do with less". That was a great "survival of the fittest" characteristic back when food was scarce, but it sure is a pain in the modern world, isn't it? (Too bad government doesn't work that way with our taxes, though. LOL)
One of the things I like about CURVES is that once you lose weight, it seems to stay off. The combination of aerobic exercise and weight training builds muscle. Muscles at rest take more calories than fat cells and muscles look much better under clothes than fat cells.

The other thing I like is that the exercise only takes about 30 minutes. I can do it in under an hour (from my front door back to my front door).
Recently, I just got back into the Curves routine. Previously, I lost about 10 pounds just doing Curves. Didn't change my eating habits or any of my daily routines. Lost about one pants size and even those were a little loose and look better on me now than they did when I was at that weight a "few years" ago. Stopped doing Curves but didn't gain back any weight. A miracle because I didn't adjust my eating habits or my daily routines after I quit. It's been about 9 months and this is the first time I've ever lost weight and kept it off. Trust me, that's a miracle!
I have just recently started back at Curves because I felt better when I was exercising. Planning to use their diet (which is similar to Atkins) because I want to lose 10 more pounds before my sister's wedding in June. Took me 4 or 5 months last time without dieting). Also, according to Curves, their diet isn't "a lifetime sentence". I tend to believe that based on my previous experience. However, I'm pretty sure that the ecercise part is "a lifetime sentence", LOL! But I hope it's one I can live with, because I really do feel better when exercise is in my life.
If anyone is still reading, thanks!
Liz - Hope your friend finds a way to lose weight that works for her. I really think adding exercise is the only way to go. Best wishes, Carol