So off we went to the fabric and craft store to buy fabric, a fisherman's net and a bag of shells. On to Home Depot to get some serious rope.
After that she was busy until the morning of Halloween, hot gluing the shells to the net and the rope, making earrings and the hair accessory. She found an old skirt that we bought when she was around ten years old (and it still fits - sort of) and effectively draped the shimmering fabric around her. It needed some safety pins and I had to knot her into the net, but in the end, it all came together beautifully and she turned into a pretty merm... uh, ocean.
She used some ribbon out of my stash for making the hair clip and then hot glued the seastar on top of it.
She loves to make earrings, and these seastars (again from my stash) were created quickly.
A close-up of the fisherman's net with all the shells she glued on.
I think she did a really good job!