Mermaid has no tail

Hey I had the same problem however I am playing on the sims 4 and it had been ages since this was posted so it might not help, my sim ate the kelp and ended up with no tail or legs in the water. I actually went in to plan outfits in a dresser and selected a tail from the 4 offered. Then when I saved and had my sim go in the water she had the tail, I spent a good half an hour trying to figure out what was wrong with my game so I hope this helps someone.