Yeah I don't know, I think only 1-2 people who saw these celebrities are TVD fans. Could be they just didn't see her in the crowd, didn't name everyone, etc. (not everyone who watches TVD follows all the gossip, so they might not have connected Nina with Derek).

Mostly I just think that in a crowd with Selena Gomez, Derek and Julianne, Lily Collins, etc., it's those types that will be mentioned, at least when spotted in LA.

So it's possible she wasn't mentioned because she wasn't at Universal, but I'm inclined to think she'd be there, with or without her brother. I think Emile Hirsch was there too, or at least, at Beacher's. He's known to frequent the place, and someone mentioned him alongside Nina and Julianne. I think they were surprised to see these celebrities while celebrating that girl's birthday, so it was like "oh, guess that's your birthday present, #happybirthdayjenna?" I don't think the birthday girl's friend would tweet an arbitrary trio of celebrities she doesn't follow on Twitter, failing to even @mention them, at the end of the girl in question's birthday night.