You must bring all your undergarments such as bra, crinoline, spanks, etc to each fitting.
You must also bring the exact shoes that you will be wearing for the occasion.
Different shoes and undergarments drastically change the fit of the dress.
Formal gowns are very close to the floor, so 1/4 of an inch heal can make a huge difference for the length.
It is impossible for any seamstress to do your alterations properly, without these items!