I know what you mean about calorie counting making you a nervous wreck. I remember for a long time living by the scale and counting calories, if you're one of those obsessive personalities like I am it starts to impair your life and even your relationships. Essentially you're replacing one crazy behavior with another. After calorie counting for that long you should have certain skills though. You know what a healthy portion of nuts/fruit/protein/carbs looks like so you really don't need the scale to measure out food. It's like learning how to add/subtract. You learn how to do these in grade school, practice for a few years and now you can just do it... you don't have to keep doing drills. Think of calorie counting as a skill, you don't have to think about it too much, just do it when you need it.
I wish we could all be like your sister, happy on the inside and not have to think about food. There is a book called "Brain Over Binge" that deals with changing how your brain responds to binge triggers. I found it very helpful and it made me realize a lot about how I get triggered to binge and how I respond automatically to those triggers when really I don't have to.
"If you pay attention to when you are hungry, what your body wants, what you are eating, when you've had enough, you end the obsession because obsession and awareness cannot coexist." - Geneen Roth