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Hmmm.
Unfortunately when you say "ball" that tends to associate dresses/skirts. ;>_>

HOWEVER.
I have a friend here who wears smart shorts a lot when she goes out, and she looks really nice. So I would say some really nice smart shorts with a pretty top would suit definitely. Or even dress pants as you said. (Sorry, British here so that only clicked that you meant trousers after I typed the shorts thing...)

And shoe wise, just go with some nice flats? Hmmm. Hair wise - how do you feel about curly hair? >_>
I say that is always nice, just some light curls anyway, nothing over the top. Just something that gives your hair a bit of movement.
Generally though, I'd say however you prefer your hair is fine.

Don't worry. :3
It's only because I'm going out every night this week that I get excited about dressing up. Soon the work will begin. >_>

Definitely have an experiment with your hair before the ball to figure out what you're going to do with it and what works. :3
Ahh. Well, not sure what it's like over there, but high-waisted shorts are always in over here for some reason.
Something like this: [x].
But then they may be too short for you maybe. I would say that trousers are probably the safer option, as I can imagine it would be more dressy there than it is here. x3