The one main diet I remember her doing was the "1/2" cup diet. You could have a 1/2 cup of anything you wanted. Doing that, plus exercise, she dropped about 100 lbs.
That makes a certain amount of sense to me. One of the FIRST things I struggled with was portion sizes. That's why recording everything I ate was so important a tool for me. It was the only way I could learn what was "normal" when I hadn't been eating normal portions for years.
Then once I had rather a good idea about proper portions for some things, I began looking up portions for other things. A half cup of ice cream or yogurt isn't as bad calorie-wise as I thought. A half cup of cottage cheese packs a protein wallop! The serving spoons at the cafeteria at work are 4 oz scoops -- half a cup. So I've learned half a cup of mac and cheese is okay once in a while... but much higher in calories than I would expect, and I have to adjust the rest of my meal accordingly. Half a cup of veggies is negligible calories. Half a cup of grape tomatoes gives me much more than I expected. Half a cup of whole wheat pasta is enough for my meal, and gives me enough "leftover" calories to enjoy a glass of red wine. Half a cup of french fries is a treat, but I choose my carbs selectively. I'll eat the burger and leave the bun if the place has good fries for me to eat instead.
And there were the nasty surprises... even half a cup of orange juice has WAY too many calories and carbs to be a common part of my plan. Half a cup of nuts is murder on the daily calorie limit. Half a cup of soup just doesn't do it for me unless it's really rich soup (like crab bisque).
I think the KIND of food choices one makes is as important as how MUCH food one eats. Calorie limits and portion sizes give us a framework, but the choices within that framework need to 1) satisfy the mouth and stomach, 2) give us good nutrition, 3) cut back on the things that we wish to avoid, and 4) be flexible enough for our lifestyle and culture.