if you feel you must show up, then refrain from expressing your reluctance to share the same air as your sister. do not talk to her at all. remember it takes two for conflict to take place. you are the kindling and she is the lit match. she comes at you and ignites the pile and boom, you have conflict. you both had a role. so if she comes at you, you choose to move your pile of kindling so she cant ignite it, then there is no conflict. the choice is yours again and again. im sorry sister,this conversation is no longer constructive, I am not going to participate in it any longer. repeat that in a calm firm voice over and over. remove yourself from the area if necessary.