[OtterXO]

I honestly think your sister just assumed you knew about the party. I have done this before where I forget to directly tell a few people about a party/get together I am having. This in NO WAY means that they aren't invited or that I wanted other people there more than them. It just slipped through the (mental) cracks. I don't think you should be offended at all but I totally understand why you would be. I definitely don't think you should say anything to your sis because then it will seem like you are overreacting. Let it go and know that if people were asking why you weren't there, it's because they wanted you to be there!!!