looking at the dress hanging behind the blue one makes me thing that you could get a wide elastic, the same colour or constrasting colour, separate the top from the skirt then join back together with the elastic in between.
Or maybe steal some fabric from the hem and add a panel on each side seam. The dress would be shorter, granted, but you would probably only need to take about 2 inches max (depending on how much you need to get a good fit. You could then use tape on the hem to minimise the amount of turn up. Just a thought.
But I agree with most of the GN replies that taking it to a seamstress would probably be the better option.