Let's start with my favorite, Forever 21....
The key to dresses is to have a full skirt and a defined waist line.
Shirts need to be a little loose at the bottom, and they need to be high enough to cover the top of your brace. The second top (the mint green one) might need a sweater over it, just for more security).
Skirts need, like dresses, to be full (meaning they're pleated, or flowy...in other words NOT skin tight), and they need a belt or elastic waistband usually. They shouls hug your waist right above where your brace hips are.
Shorts need to be a size or two above what you usually wear, and should be loose. You can wear tight shorts, but you'll want a long shirt to cover them up!
I hope this helps! All of these clothes are available from Forever 21's website or store: