I would say one half has her with the hat and cape, looking high and mighty (or great and powerful) with a colorful show going on behind her (like when she appeared in ponyville) and the other half would have no outfit, and she would look sad, lonely, and longing for friendship with a plain, dull background
As to how she's portrayed, what I picture has already been said multiple times below - confident, determined, smiling Trixie with her hat and cape on the left... and as for the right side, maybe a scared or threatened Trixie minus hat and / or cape.
So! The only new thing I can suggest is what the text will say. With the above in mind, I picture her saying:
(Left side) "Now you see" (Right side) "my true" (Bottom) "POWER."
I probably don't need to explain why, but I will just for the sake of being a windbag. It could make sense on both sides: on her left (confident side), as to say "Look how powerful I am!", as well as on the right (threatened, afraid) as if to say "Oh no, you've realised I'm not that powerful after all." Hence - "Now you see my true POWER".
If you were wondering what I meant when I said "makes sense on both sides", I just mean the different ways in which each of your Two Sides makes its impact:
1. Two Sides than can be read on either side and make sense. These are my favourite kind. Examples are Twilight Sparkle (Everything must be PERFECT) and Rainbow Dash (I'm not afraid of anything except FAILURE).
2. Two Sides in which the last word makes the greatest impact. These are also quite effective. Often the first part of the sentence fits more with the left-hand side, where the last word pushes you to see the right side more. Best example is Applejack (I'll show you I don't need your HELP).
3. Two Sides in which the text makes more sense on one side than the other. Possibly that the right-side and the text are 'buried beneath' the left hand side. An example would be Princess Celestia (One thousand years of REGRET) and Discord (Get ready for a storm of CHAOS).