Hello, and welcome to the Gift Gathering - Thank Yous & Gifting Thread of the Sims 3 forum. There is so much to do and see that it's a little disorienting, isn't it? Well, this is your one stop sh...
You need to uninstall the custom skin. Open your launcher and try to find the skin in the installed list and then uninstall from there. Just deleting the sim will not get rid of custom content