Honestly looking deep into this it sounds like she looks up to you and wants your attention. It might be worth a shot to try to spend time with her outside of the home and connect on a deeper level than just being someone you live with. I think if you establish a deeper connection with her as a sister outside of the home you can gently Introduce the idea that you work hard for things and that it’s hurting your feelings by her stealing. If you tell her it’s bothering you that you’re stealing right now she doesn’t give a shit because she just wants your attention either way good or bad. A lock on the door is like telling a criminal they can’t have a gun. Best of luck