As I said, you know Unix is not Windows. If you can *really* fool a Windows user a Unix desktop is Windows, then he/she is probably not a real Windows user.

Maybe set up a test machine for her, allow her to play in anyway she likes. Preconfigure a wallpaper/theme that is sufficient to attract her eyesight on that machine. Just use all sort of ways to make her feel that it is interesting, beautiful and approachable, then she may be willing to try it.