If it's an evening wedding, go for darker colors, maybe a cocktail-type dress. Something like this?
http://www.gap.com/browse/product.do...scid=411181002
or this
http://www.overstock.com/?page=proframe&prod_id=1651212
We pear-shaped women look fabulous in full skirts.
If it's a daytime wedding, go for a sun-dress feel, maybe something floral and "flirty," maybe something like this:
http://www.overstock.com/?page=proframe&prod_id=966951
Or this:
http://www.overstock.com/?page=proframe&prod_id=1814005
Or this:
http://www.overstock.com/?page=proframe&prod_id=1800048
Something like this would be a safe option for either time:
http://www.overstock.com/?page=proframe&prod_id=1814000
Don't wear white to a wedding (heh) and if the bride is EXTREMELY traditional, don't wear solid black, either. (It's seen as a mourning color, not for weddings; though these days just about anything goes and hardly anybody really cares what the guests wear).