don't you have any supports? do you have a counselor? you can always call a crisis line, you don't have to be suicidal, they are there to talk. you can PM a community liaison.
it is difficult knowing the appropriate things to say to you with the limited info you have given. however, your needs should be the priority. do you know what those needs are? you should be living for yourself. it doesn't matter what your sister thinks of you unless her opinion of you really matter. sometimes we work so hard pleasing others that we really lose ourselves. if she is hurting you, you do not need that in your life. it is ok to remove yourself from that situation. it is ok to tell her how you feel. if that is too triggering, then you can still remove yourself from the stressor and explain it later when you are stronger. you don't have to disappear without an explanation. you just say that you are struggling right now and need some space. you don't owe more of an explanation that that. say you will explain more when you can. just ask to have your feelings respect. hang in there.