How bout instead of starting with the Master-Cleanse right off you start with that change in diet you're talking about. This will do 2 things first it will act a as a precleanse and get your bodies to gradually start detoxing so not only will it minimize any detox symtoms you might get on the Master-Cleanse but you'll also know whether she will be committed enough to use the Master-Cleanse for weightloss.

Here's the reasoning behind starting with the change in diet first . First you will be setting up a good example/presecedence on an impresionable 13 year mind about a healthy lifestyle rather than ingraining a quickfix mentally that in the long wrong will always lead to failure. Then there's the part that the MC or any fast will slow the metabolism and if she goes back to eating junk not only will she gain any lost weight back but possibly even more than she lost again setting her up for failure.

When I say healthy Diet I'm not talking portions here we are talking quality. The best investment you will make for both you and your daughter and a great start towards a healthy life style that will include safe and effective weight loss is to start juicing veggies. Not only will that start you and her detoxing and lossing weight but you will be getting amazing amounts of mega doses of readily absorbable nutrient, vitalims minerals and on and on. You see the way it works is the body has to turn everthing into juice to beging with in order to absorb the nutrients so when you juice you have already done 80% or more of digestion and drinking a 12 oz glass of veggie juice will be the nutritional equivalent of eating 15 or 20 lbs of veggies. There are bunches of recipes for many delicious juices

I suggest that you start educating yourself on juices and start leaning towards using less and less flour based products, dairy and sugar. Join a gym and start getting regular exercise. Last but not least start drinking 1/2oz of water per pound of body weight daily.