There are so many ways to take this tutorial and adapt it to your taste. I used 3/4 inch elastic because that's what I had laying around. If you want to get it closer to the J. Crew dress, go a little thinner. I also made my straps a little wider, but you can easily suit the thickness of the straps to your own taste.
Needle & Thread (for your flower)
We will start by making 2 panels of fabric. Measure around the chest. Add 1 inch to this measurement. This measurement will be the width of each panel. Measure the length you want the dress by holding your tape measure from the chest down to the point you want your dress to end. Add 2 1/2 inches to this measurement, and that is the length of the fabric panel you need to cut out. My little darlings chest measurements were 21 inches and the desired length was 19 inches. So I had 2 panels that measured 22 inches wide and 21 1/2 inches long.
Put aside leftover material for your straps and flower.
Fold your fabric again 1 1/2 inches. Sew around 1/4 in. from bottom of fold but leave an opening for the elastic.
Here's where we start to run out of pictures.
Congratulations, you just saved $80.