Many people don't know what a healthy portion size looks like. The Australian Healthy Food Guide website has a free downloadable PDF Portion Poster which I highly recommend looking at. According to the Eat for Health website, 14-18 year old girls need the following:
Vegetables... 5 serves
Fruit... 2 serves
Grains... 7 serves
Lean meat, poultry, fish, eggs, nuts, seeds and legumes... 2 1/2 serves
Milk, yoghurt, cheese... 3 1/2 serves
Active, older or taller girls can have 0-3 extra serves of food or treats.
It would be a very useful exercise to keep a journal of what you eat and work out how many portions of each food group you eat per day.