This is the response from the bridal shop. Ignore the stuff about the length.
My sister put the dress on and before she even got in the wedding car it broke. Zipper stayed at the top and the zip just broke apart. She had to be stitched into it while the car was waiting.
"As for the zip on the maids gown we give all our customers a second fitting or the chance for them to try all gowns before they are removed from the premises. This is to ensure that both the customer and [bridal shop] are happy that the gowns are in perfect condition and you are satisfied with the alterations when they leave the shop. If you were unhappy with the length of the gown we would have been more than willing to re-hem the gown at no extra charge before you took the gown away.
Unfortunately we cannot take responsibility for the gown once it has left the shop."
Our contract is with the shop. The goods were not fit for purpose. They're wrong about not taking responsibility aren't they?