User blog comment:StoryGirl83/The Sophomore, Book 2, Chapter 10 - Party Guests/@comment-34381956-20180225021648

Edgar, Leila, Tripp, Chelsea, Claire, and Grant weren't at my party either. I usually skip the diamond choices in Sophomore (actually, since I accidentally reset my game data like three weeks ago, I think I've only spent diamonds to spend time with Zig's family this week), but I think some of them let us spend time with people who aren't in the friend group. If you have enough of those for a person, that might lead to them being at the party. For example, Grant didn't come to my party, but he might have been there if I had spent diamonds to invite him to stay for dinner in chapter 4 and/or spied with him and Zack in chapter 9.