I used Burda Kids pattern 9649 . It's a very good pattern with easy to follow instructions and clear illustrations. However, the sizing does run a bit large.
I made a few modifications- a peter pan collar instead of a ruffle and extending the skirt lining to full length. I was able to make the gown entirely out of fabric from her wedding dress. The only thing not original to her wedding dress is the snaps.
I also made a matching bonnet (included in the same pattern).
They plan to use this gown for all of their children so I embroidered her daughter's name on the hem of the skirt lining, that way they can add each child's name as they wear it.