If you eat 1200 calories a day and burn 300 via exercise, that would mean you're only "netting", 900 calories for the entire day.
How much weight are you trying to lose per week ? If you entered in a value of one pound per week, the software then calculates based on your daily activity how much you should eat each day in order to lose that one pound. If the software says you should be eating 1200 calories per day. That means that you should be eating 1700 calories per day just to be able to maintain your weight.
In order to safely lose one pound per week, it is assumed that IF a person decreases the amount they eat by 500 calories each day, then in seven days that will give them a total loss of 3,500 calories or one pound of fat. one pound = 3,500 calories.
So, if you are eating 1200 calories per day, you've already had that 500 calories deducted. Now, you're increasing that daily deduction by another 300 calories. that means that on days you do your WATP DVDs, you have a total caloric deduction of 800 calories ! That's not enough calories to keep a grown woman healthy.
Studies have shown that the minimum amount of calories a woman should eat should be 1200, not including exercise.
Eating too little can hinder a person's weight loss, not help it. I know this is going to sound strange, but a person has to eat in order to lose weight.
Now, I'm not a dietitian, so please take anything I say with a grain of salt. But, you might consider eating a bit more on days you do the DVDs so that your body isn't starved of the calories it needs to be healthy. Because 900 calories NET a day really isn't enough for a grown woman.