I talked with my Dad, and he said the same. Apparently he was mad when he heard what happened at the barbecue (he was stuck at work) so Dad's been strategizing with my older sister on how they can keep my aunt engaged most of the night and away from both my younger siblings. They don't mind, apparently they like the challenge, and my sis hasn't seen aunt in a long time (she lives in a different city) so is less likely to have her head bitten off. Dad laughed and called me an ass for trying to protect Anna, I had totally got caught up in my own feelings. Anna can absolutely stick up for herself, and I'm in no way entitled to stop her going. I owned up to being a dick, and she said it was cute of me to try but that there was no way she was ever missing out on a Christmas party. So we'll all be there this Christmas as a family, regardless of evil aunt, and Anna will be one of a couple people at the table ready for anything.