Taking in a wedding dress that is too big is quite common; in fact most dresses that come to me for alterations come in to have the side seams taken in. Letting out a dress is a bit more complicated because you are limited by the amount of fabric in the side seams.
She needed more than 2 1/2 inches added into the hipline and surprisingly I was able to meet the challenge. We lucked out with the princess seaming and bigger than normal seam allowances. It is tight but it zips and she looks fabulous don't you think?! (and she just got home from work before this final fitting)