I am a Disney Princess Lookalike, but I'm 5'8. If I am exactly what they're looking for, but 5'8, could I still be a princess?
It's possible, but remember that there are plenty of girls out there who are also exactly what they are looking for and are the right height as well. Also remember that you'll never know exactly what they are looking for until they tell you so. I'm not saying that to be mean, honest, just to let you know not to get your hopes up (though it appears you're being realistic about it by asking!!).
You also have to pass the movement and animation tests before they consider you as a princess. Having been in one of those auditions, let me tell you, all it takes is one slip of the foot to knock you out. In my audition I had my eyes locked with one of the casters who was beaming at me as I danced their way. Then I lost my footing a bit, looked down to fix myself, and when I looked back up the smile was gone and she was scribbling away.
The best way to have a good shot, in my opinion, is to take a dance class or two, practice big and realistic animations, and most importantly, practice that princess smile! Don't wear make up to the audition, and be dressed comfortably. Whatever you do, don't dress yourself up. They need to see you sans make up to consider you properly and if you're exactly what they're looking for you'll look like a princess in easily moved in sweats!
Keep dreaming and hoping, and you very well might be a princess! Good luck!