I bought a full length dress for my brother's wedding in monsoon, got many compliments on it. They also have a selection of "bride" style dresses but not full on princess gowns (upstairs in the shop on grafton street), I don't know if your sister is even planning on wearing white but she might find something a bit more low key and more her style in there and you'll more than likely find something suitable too. They can be a bit pricey, their sterling prices and euro prices don't match up, you'd probably be better off ordering from their website, their sizes are right, when I say that I mean if it's marked as a 14 it is actually a 14. I've worn my dress a lot since then and it's still in perfect condition (bought it two years ago). Good luck!