Hi I'm Danielle and I'm turning 13 this year , I need to lose at least 20kgs . I am 66.7kgs and 1.65m , how can I lose that weight in 3 months? Please help I really want to lose weight so I can look like Victoria Justice before my birthday in September!!

Okay... your BMI looks to be about 23.7 if I did the conversions right, which is normal. If you were to loose 20kg (and be 46.7kg) you'd be dead not to mention severely underweight.
Are you sure you got your numbers right?

There is no realistic or safe way you could loose so much weight is such a short space of time.
You are currently well within the normal range for your age and height.
In actual fact drastic weight lose at this time in your life will cause serious health issues.
You are still growing..

You are growing. You seems normal at current weight. Don't try to look like someone else. Try to develop your own personality. This is time to learn and enjoy.

The average weight for 13 years old and 1.65m is 52kgs. You need to lose only 14kgs for maintaining a fit body. In order to lose this weight naturally, your intake calories must be lesser than burning calories and do exercises regularly.