If you aren't too sore, it is ok to exercise daily. That's what are bodies were made to do. I have been exercising daily. Just not going hard on my body all the time. If my muscle is sore I rest it, but it will usually feel better after a couple days of being worked out. Once you lose the weight (ONLY if you lose the weight slowly) you can cut back on your exercise and STILL eat healthy, and maintain the weight. Your sister is talking about fad diets, or crash diets, where you lose a lot of weight fast and practically starve yourself on some ridiculous diet where you prepare things that no one has ever heard of...and you lose muscle and yeah, you always regain by using that method. But this way I am telling you about is the only TRUE way to lose FAT (Not weight, FAT) By eating good you give your body the right fuel it needs to work, protein, carbs, and good fats. And your body will eat what you give it, instead of the muscle. And you will build muscle through weight lifting. Then doing cardio will burn fat. You will never see results right away. But little changes in the appearance of your skin could happen in a couple weeks, then by a couple months you could be in the comfortable 130's.