Why I refuse to speak to my sister

Because the last time that we talked, she was in her bathroom, washing clothes because washing clothes  was more important to her than talking to me. Just talk because I'm washing clothes, she said in a dismissive tone, as if what I was about to tell her was something that would only need half her attention, like when you tell her, hey, I'm going to the market, do you need something for me to buy? No, that was not the kind I was trying to talk about. In my mind, I revised and reviewed several ways to tell her how I knew she was ostracising me, her kind of a power play, something that I saw other people do to me countless of times but never expected it from a family member.  Also, I wanted to ask her if she was talking about me in front of my boy? Why is my boy behaving like that? But I did not know how to bring this up so I talked about other things and realised we were replaying scenes we did in childhood; her being allowed to do everything she liked with impunity while I was not allowed to complain because I was older by one year and five months. Every time she did something to me, Ma, who was now in her sickbed, said I should not complain because I was the older one, I should just let my sisters be because they were younger. 

So, while she was yelling at me, "you always have what you wanted!" and me, dumbfounded, saying, "whaaat?" and could not even say a word. When I said, why are you not including me in your discussions and your plans? Both of you talking to each other, excluding me as if I were not a part of it. She replied, "Whaaat? Do I have to ask your permission to give the medicine to our Mother?" As if that was what I meant. So as she continued talking angrily in her bathroom, I quietly stood up, opened the door, walked away calmly and felt sharp pains shooting from my left arms and left shoulder as I reached the potholed streets a few paces from her gate. It was my body's way of telling me it was such a really terrible experience talking there with my sister.  I should not do it again.