My Annoying CopyCat Sister?

You cannot make her stop unless you banish her to goblin land. Unfortunately she is doing what a lot of little sisters do. Wile copying you she is looking for her own identity. I think you should worry less about little sis and once she see that it no longer bothers you she will most likely stop. The more you fight her she will continue. Everyone learn their sense of style from someone so we all at some point copy our style from someone else. Time will change things. You have to be patient and let her outgrow this phase. Happy New Year