Max You should target is 1% of your body weight per week and that would be when you are considerably overweight n have a lot of fat to burn. Your ideal weight is 135 with a range of 105 to 153 so you should probably be targeting 2/3 of max or 1lbs.
You should also be eating well and try to get your weight loss by exercise.
As to your question, don't worry about flabby skin. At your age your skin has elasticity n will adjust to weight loss. You could use a moisturising cream regularly to prevent strech marks.
If you try to lose 3-4 lb per week, or even continue with the 2lb per week, I think we can guarantee rapid regain -- which is one of the things which contributes to loose skin.
Unless you weigh more than 200lb you should not be losing 2lb per week -- and as a teen who is at a healthy weight, if you are losing 2lb per week, I'm guessing you are either under-eating or over-exercising.
The minimum recommended calories for an overweight active teen female is 1800 calories; if sedentary, then it's 1500. You are not overweight -- if you are active at all, then you shouldn't be eating less than 1800-2000 (with 2000 the better idea). Slow weight loss is generally more effective in the long run, and more sustainable. If you have not been clinically obese, you are also less likely to have loose skin if you lose the vanity pounds slowly.
