I am sorry, I intended this to be a reply to your post and I put it in the wrong place.

You can stay on it longer than 2 weeks but carbohydrates are needed for good health so, as with any diet, use wisdom. What does Dr. Atkins say about this? Even in his carb counter he encourages that you take care of how the diet is followed. The diet is formulated to retrain the body to consume the proper amount of carbohydrates so that it does not impact blood sugar. Has your sister had any blood tests done while on this diet? Having your blood tested periodically is a part of doing this.

Black57