Once I gathered the waistline by sewing a long stitch through the top and then pulling it, I decided to make a bodice using some of the leftover lining of the dress. Making the bodice to a little girl's sundress is pretty simple once you figure out the gist of it. The shape above pretty much sums it up. I cut my bodice as one large piece, but I added dotted lines to show where to make the seams if you want to make it using three pieces. I cut out two of these shapes, sewed them together and flipped them right side out and bingo-bango, you have a bodice.
I sewed the bodice to the top of the gathered skirt and from here I was pretty much done. Next was deciding how to make the straps and close up the back. I decided to use the ribbon that was originally on the dress as a tie in the back to make some straps, and instead of a button in the back to close it, I decided to punch in some eyelets and tie it. This seemed easier at the time! I recommend a pair of eyelet pliers to anyone who is routinely crafty :-)
So here is the finished dress on my baby girl.