Seasons,
It is such a strange feeling, once you know about N, then when you interact with these people, you can almost predict what kinds of things they will pull on you. It's like there is a script somewhere that they have all studied. The details vary, but all the tricks and mannerisms come through almost every time. It makes my head spin sometimes, but it is better to know the truth. Then you know you're not at fault here.
For a little while with one of my Ns, I would think and think about how to phrase things so that I would know there would be a response. This is with email. Because normal emails were ignored. Purposely I believe. But come up with something complimentary enough and the response would be immediate and almost gushing. It was fun and I tried it about three times, then it got boring. It was more like pressing a button and hearing the buzzer go off. No real exchange of ideas. No real relationship. Just a mechanical cause and effect.
We all need more than that from the people we care about. You will be happier without your sister. Though it must be a relief that she doesn't have cancer, a healthy sister is still N. And that is unhealthy for you. She will always find sources of supply. It doesn't need to be you anymore.

Go for it, seasons! It's your turn to have your life back.
Pennyplant