Hi Doh, is the issue with your sister that she comes over unannounced? If so, rather than saying "I don't want to see you", which sounds quite global and rejecting, how about saying something like, "I really need time for myself right now, so I'm asking everyone, both friends and family, to give me warning when they want to visit, so we can set a time up that works for us both. Can you call the next time you want to get together?"

Would that work?