What you need:
Open the side seams of the nightgown 7 1/2 inch up from the bottom. To accommodate the tail fin, fold opened seams in on an angle so that the bottom of the nightgown is now 11 1/2 inch wide. Starting at the bottom front of the nightgown, overlap and glue a row of flattened cupcake liners. Repeat until entire front side is covered. Turn over, and repeat on the back. When finished, add a final layer to each side, just above the 7 1/2 inch opening. Enlarge shell top and tail fin templates as needed, and cut out. Trace onto green corrugated paper, and cut out. Decorate with glitter glue. Use a glue gun to attach to nightgown.
To make starfish barrette:
Glue a store-bought starfish to a barrette or hair comb, and place in hair.