Thanks MMQC: It sounds dreadful.
I would agree with jmoose - if her father was known for grand standing with the hand stands at parties and her friends rolled their eyes along with her - no big deal.
Instead, I gather SL feels humiliated at her party in front of her Wagner friends - some of whom she may not have known that well? Perhaps had never been to her house before?
The BF/F is not there, or a part of the party, and her father creates a scene that causes her to create a scene -
I wonder if there were mutual friends of SL and her BF/F at the party and if the "buzz" about the fight afterwards got back to her - made her feel embarrassed, inferior, mortified.
-Or, if feedback got back to her through her BF/F? "So and so told me what happened and you did what to your father?" So and so thinks your father has issues.. etc...
IMO -The party's significance is in its close date (EOA) preceding her disappearance along with the fact that she is characterized as depressed on the PR.