Kate was there as one of Natasha's plus ones! She dressed nicely but not excessively formally. She was raised in high society and she knows what she's doing around wine. I doubt she made it through the list, but she tried her hardest.
Much socializing and thanks to Torunn and Thor! She reeled it in a little bit tonight because this was not a house party, but she spent plenty of time with her people and probably yanked Natasha and Yelena (if she was there) out onto the dance floor if they'd allow it.