I am petite, same height as you, and I got a regular size dress from DB and had it altered. I wanted the train though, but I did have the material cut out and just kept the lace for the train. I bought mine at the store off the rack, so I got mine really cheap. I think they can get them so quickly because they sell them off the rack a lot, so I would believe they can do it that fast. Which dress is it? Can you show us the link. I say go with petite and get the train cut off later, its not a big deal to do that really. This way you know it will be what you want and it might not need to be hemmed at all.