First off, I doubt she is paying extra and eating natural peanut butter (inredients: peanuts, salt). I am sure she is paying 1/2 the cost and buying jiff or peter pan etc - loaded with hydrogenated oils, chemicals, and SUGAR. There has been a lot of research that show that though high in calories and fat - nuts, seeds, and avocados do not lead to weight gain, even if they increase calorie intake.  Just one of many sources available Protein bars on the other hand -  basically sugar loaded candy bars, with probably unneeded levels of protein for her limited activity output. I doubt she is doing tabata protocol squats or bench presses.