If your Sim looks "chopped up" or has red/white question marks, you might be missing the mesh file. Check the creator's page to see if you need to download a "required" base file first.

Relaunch the game for the dress to appear in Create A Sim (CAS) . Troubleshooting Tips

Often follows a modern or "Maxis Match" style, blending seamlessly with the game's original art direction.