according me u shud get ready like unmarried girl if ur in laws(sp MIL lol) ok wid dat coz i was in da same situation as u r now n i wanted to b prepared lyk unmarried (coz i dont like heavy jewellery n stuff) but my MIL wanted to see me in heavy jewellary n dress :(...
so i went in the middle way like heavy suit wid light jewellery
errr first off lets address the pesky little matter of semantics ...
nikah = married : in the eyes of law (religious and otherwise) you are considered married after nikkah :)
so like it or not ... you are married ... now you can say you haven't had rukhsati yet and that would be totally accurate.
now the original question: don't dress like anything. Dress according to your age, physique, complexion, personality and the occasion ... regardless of your marital status
I think you should go with whichever you prefer, like I personally would love to dress up heavily, but because I'm young and unmarried it would seem wierd to do so, so you should go with whichever you feel more comfortable with.