Measure the person who will wear the costume. Measure and write down the height from shoulder to foot, the width of the shoulders, bust, waist and hips, and the length from the shoulder to wrist.
Make a pattern using the measurements. Draw a sleeveless shift dress shape on a piece of tissue paper meant for making sewing patterns. Make sure the shoulders, bust, waist and hips are the correct width, and make sure the shape is the same height as the measurement taken. Don't worry about sleeves, they will be made later.
Fold a two yard-piece of white fabric in half lengthwise so you ave a double layer of fabric. You can use any white fabric you have available, though a material like poly-satin gives a nice sheen and is still affordable. Attach the pattern to the fabric with straight pins and then cut out the fabric by following the traced pattern. Leave an extra 1/8-inch margin around the pattern for seam allowance. You should now have two identical dress panels.
Sew the two dress panels together on the sewing machine. Sew the sides of the dress panels together, as well as the top of the shoulder straps. Leave open the bottom of the skirt and the arm and neck holes. Fold over the bottom hem and sew a seam to make a nice edge. Do the same for the hem of the neck.
Cut out two identical strips of white fabric to make the sleeves. Make sure the strips are as long as the length of the costume-wearer's arm, and are about 14 inches wide. Fold the strips in half lengthwise and sew a hem along the edge. Fold over the bottom edge of the sleeve and sew a hem. Sew a sleeve to each arm hole of the dress.
Turn the dress inside-out so the clean edges of the hems are on the outside. Measure the black lace and attach the appropriate lengths around the bust and waist of the dress in any pattern you desire. Attach using the sewing machine.
For Eliza's parasol, paint an umbrella with white spray paint and let dry. Attach some leftover black lace trim along the rim of the umbrella using a hot glue gun.