I have to agree with Elsah that restricting too much may not be a good approach, especially if you can get her to increase her activity levels along with cutting the obvious junk such as chips, candy, pop and such.
I'm also not sure that "dictating" the change is a good approach, either, especially with a teenager. Having a willing participant makes it that much more likely that she will stick with it during those times when you are not looking over her shoulder instead of cheating and eating whatever she pleases as soon as you're not looking.
Some of the snacks I give my kids at the 100-125 gram of carb level are:
Yogurt (no sugar added) with berries
Smoothies made with plain yogurt and berries sweetened with Splenda
Low carb Ice cream
Sugar-free popsicles
Veggies with dip
Nuts
Sugar-free pudding made with Carb Countdown milk
Celery with natural peanut butter
Whole-wheat crackers with cheese or peanut butter
Pepperoni slices
cheese sticks
Apples, oranges, pears (lower glycemic fruits)
Occasionally a small amount of popcorn (not the microwave kind!)
With summer coming, I may offer ice cream floats with diet pop and a scoop of low carb vanilla ice cream.
I hear that Raspberry or Orange Diet Rite with low carb vanilla ice cream is yummy!
Once she sees the results, both in her weight and in how she feels, she may find herself hooked!