awwwww- what a sweetie! depending on how adventourous youu are, you could try taking apart a shirt of hers that she likes the fit of, but (preferably) doesn't wear anymore, check out the fabric store for some inspiring fabrics, then lengthen or shorten and design it to compliment the skirt you had in mind and of course, the wedding!  Just remember that if you use a knit shirt for the pattern, making it of woven fabric wont work out right (speaking from experience... opps )  Hope this helps and good luck!