Venting about work

I hate my coworker more then I thought I could hate anyone. She doesn't do any work and tells customers my business (that I smoke cigarettes/had a mc/ etc) after I've told her (almost on a daily basis not to). There's only us 2 employees and our boss. Problem is she has been there 3 years, since she was 16. I'm 27 with a 4 year degree that isn't needed for the job. I've only been there 8 months or so. I get paid the least, work more hours then her or the boss and do all the work (literally). I get 2 days off a week, Thursday and Sunday and she only works Thursday to Sunday. Doesn't come in when she's supposed to, doesn't do any work in general. Ahh I'm just fed up. The boss can in today to tell us that I have to work Sunday to do inventory. I'm going to re vamp my resume tonight and start watching the job ads for a better job. But I'm going to strangle her soon if I have to continue working with her. Any advice? Thanks for letting me get that out.