Hi A.:
I Come from a family of 5 girls,so much of what you explained, was typical for our household.You wouldn't believe the petty arguments we got into.It sounds to me, that your daughter that lives there year round,feels a little put out,when it comes time for your step-daughter to visit.Some of her attention automatically switches to your stepdaughter,the moment she comes into the house. your stepdaughter,knows her presence,urks your daughter, and so she is on the defensive before even arriving.I would bet,she dreads the thought of visiting,because she knows, that there will be conflict.My mom and dad, went crazy for years,trying to intervene,whenever we would taunt each other or argue over whos turn it was to do the dishes,or whos hair was longer,or who had one more helping of cake!! All 5 of us girls fought like crazy,but we loved each other very much.Siblings are always on that fine line of love and hate!They will drive you insane, if you don't start letting them iron out some of their own differences. Alot of their petty arguments,are for your benifit.An act if you will.They want to test you both to see if you'll side,and with which one? I could see you stepping in,when they were toddlers,but they are young women now,and they shouldn't need referees,each and every time they disagree.If they want to argue the price of tea in China, tell them to go in the other room and discuss it, so as not to disrupt the rest of the family.They can talk till they go hoarse. lol. If your sitting at dinner and they start,tell them to excuse themselves and after they finish their debate, they can return.Don't allow them to disrupt things,or anger you. As soon as they realize, that neither of you are going to (Take sides) or involve yourself in their pettyness, they will begin to ease up on one another.The very best to you and your family.