Well... I don't know. It seems to me you've pretty-much ruled out anything that one might ordinarily think of. (Perhaps some other members, here on PC, will come up with some new creative solutions.) The only other thing that occurs to me is to try to arrange your schedule such that you spend as little time as possible in your sister's proximity; that and perhaps consider just going off of any & all social media where your sister could find you.

The thing is, you've pretty-much painted yourself into a corner here. There simply aren't likely to be an magic solutions I don't believe. In my own situation, I recall once saying to a therapist I was talking to: "I know what my options are. I just don't like any of them." There comes a point where one simply has to accept that the options are what they are. One either chooses one of them, or accepts that circumstances are just going to continue to be what they are... unfortunate as that sometimes can be. I wish you well...