the call that broke the camels back

I guess I really don't know what to say or where to start because there's so much. Honestly I would just have to start from the beginning.
This isn't a sob story or a "feel sorry for me" or anyone rendition of what has happened. It's just the truth and that's the only way I can tell it.
I'm the oldest of three girls and when I was only six (if that) my father cheated on my mom and left us to fend for ourselves. Truthfully he and that are a whole other story but this one isn't about him or his stupidity.
After he had left and started his torment upon our lives the therapist had told my mom that we each would react to it all in a different way. My baby sister and I were very angry and would loose our tempers often. Sarah,the middle sister, would create drama with everything. Sarah was the one I chose to take my anger out on. I know and will admit now that I was very cruel to her growing up. She learned how to retaliate but being the oldest I would always win. So Sarah had taken on the defense that she thought she was smarter than me. She would use that to her advantage and would put me down. I'm not a genius by any means but I'm not even close to being somewhat dumb either. I'm fairly intelligent but because I dropped out of school and earned my GED she thinks less of me in the sense that I'm not that smart.
Dropping out was the smartest and only thing I could do. I was already homeschooled but because of the homeschooling system, in which there is none, they could care less of what happened to me. So being smarter than where I was suppose to be and having learned the higher education I decided to stop and get my GED as soon as I was able. I think it was at 16.
Anyway, that being beside the point. For the last 2 and some years I have been trying to correct my relationship with Sarah. I swear my efforts are useless because she still treats me as though I hate her. Since that is currently what she thinks. It makes me angry because she doesn't like to be told any criticism, an honest opinion or pure concern she'll become upset and won't listen. I've learned some time ago that I can't tell either of my sisters what to do but when it come to talking to Sarah she acts as though I have lived in a box with each of my blessing handed to me on a silver platter never having to gone through any turmoil. Therefore my opinion means nothing because apparently I have experienced nothing.
We're not close but truthfully it's because we're so different in our personalities. Yes, it has to do with the fact of how I treated her when we were kids but it also has to deal with how she treats me now. I have cried about it many times and even tried writing to her letting her know how I feel. But it seems pointless when she's not willing to meet me in the middle. I still love her and I'm still trying to reconcile with her but she does not make it easy.
My mom told me that the other day she called crying about how her and I aren't that close. All I could do was tell my mom, "what can she expect?" I know it probably sounds heartless but I did go on to tell my mom what she already knew, that I was making every effort but with Sarah it's like taking 1 step forward and 2 steps back. And again I know I was cruel to her. It was my way of taking out my anger from my father. I feel terrible for it now but it was how it was. I can't change it. All I can do is make up for it now.
My mom called me her "scapegoat" on the phone. This is because when she talks to us about things she's excited about and show concern about them she'll get angry with me even though my mom and I said the same thing. What should I do? Just bite my tongue and when the authorities find her body do I wait to tell her in the after life, "I told you so."? And really she has put herself in that position many times because she is so naive and thinks everyone is good. But I don't want that to happen. So I'll just continue looking out for her even if she does get angry with me.
This all probably sounds like every bad relationship with a sister. And maybe it is. I'm not sure.
I guess the only thing I can do is keep trying to make things right and sooner or later she'll come around.
Hopefully.