I'm afraid she is so far gone right now, that I am pretty much done trying to actively reach her or maintain a relationship. I will see her at the family reunion in August (she will be late, because they do their field service and Bible study before making the 2 hour drive to the party). I may run into her occasionally at my parents' house, but she usually leaves shortly after I arrive. I will keep my word, and be loving and kind to her, when I do see her. I make a point to say hello and "I love you" to each member of their family at the reunion. The reaction from my brother in law (turns stiff as a stone while I hug him in front of others) makes it all worth the effort.
I have been honest with her, and I do not expect her to reply or explain herself. My sister has washed her hands of me.
I am going to mention this to my mother, who I should have the opportunity to see this week. She was recently hospitalized for a chronic illness/infection that she has to monitor and treat regularly. I have noticed that my mom has been more actively texting and emailing me, and we have had some good conversations on the phone. I'm taking advantage of this opening, to try to rebuild some of the lost connection with her. I used to be very close to my mom, but she now has a dual personality. Lately though, her natural persona has been showing itself, and I have enjoyed a few good visits with her. My kids have had a good experience with all this, and I am pursuing it as much as I can. I will not bring up any more JW stuff with her, unless she does.
When the issue comes up about the way my sister and brother in law are shunning me, I simply tell my parents that all is forgiven. I am not the one who has a problem. I say, "They are just trying to do what they believe is right. I forgive them." The stunned look I get from my dad when I say this, is very telling. (Does Satan forgive JW's ...??)
My niece (12 years old) saw me last week, when I visited my mom at the hospital. She was there with her dad, my brother in law, who would not make eye contact with me. He was bizarrely familiar with my kids, however, and seemed surprised that they were afraid to talk to him. My niece kept looking at me, and smiling at me. I think she knows what is going on, and I have heard murmurings about her being "rebellious." She is not yet baptized.
My mom is a very weak JW, who made the statement to me recently, "Maybe I should not have gone ahead and been baptized." (!!!!) I think all the characters are being put into place, and prepared for the eventual rescue of this family from the WTS. Either that, or we will have front row seats, when they all follow "the instructions that do make sense from a human standpoint." (November 2013 Watchtower) Time will tell.