fun colors, you want to look like you are happy not at a funeral so colors! you look like you would look really pretty in a bright blue or dark orange. something you can dance in so it can be around knee length and loose but do not dress too revealing because all the focus should not be on you lol i am looking for dresses too so i have an example for you http://funadvice.com/r/161aqc6rs6b
I would go for something elegant..you don't want to take attention from your friend, but you also want to show that the occasion is important to you and you take it seriously. Wear a classic shape that you know works for your figure.
Elegant, classy, (nothing all white, or even if you can nothing white.) Usually you dont wear white cause it takes away from the brides dress. Summer colors.
big floral patterns are ver flatering. possiblyy a haulter top, or something with a nice belt for accent
Colorful, bright, celebratory....have a great time !