My little sister looks up to me but i treeat her like crap?

she is 9, i'm 12, she's always follwing me around, wanting to hang out with me and my friends but i tell her that until she stops wetting her bed she can't (she still wears diapers and is embarrassed by it at a slumber party which she intruded on i pulled her pjs off and exposed her diapers to everyone and jnow everyopne just calls her diaper girl) anyway she always wants to be arounbd me but i just tell her to go to mommy or get lost, or to leave me alone. i have stolen some of her clothes, her stuffed animals, and dolls when she comes to try to get them back i just push her down and sometimes she wets or poops hersel;f so i laugh at her more. i wish i could just get her to leave me alone for good because she's annoying and a big baby. what can i do?