For chill, I would top it with a short, white colored wrap. Or you could do a long-ish white blazer.
I wouldn't accessorize too much bc it'd compete w/ the dress graphics. Maybe some lucite or clear bangles like Alexis Bittal.
And I think heels would be too much (plus you'll be on your feet for awhile) and I'd be more apt to go with a flat sandal IF appropriate with however formal her wedding will be. If not, strappy high sandals or a wedge.