People think she was just a hateful snob but she wasn't. Yes, most of the people were a bit snobbish but Vivian had friends and was the one who planned that party that she told Elle was a costume party. She mainly had a problem with Elle because she was Warner's ex-girlfriend. Vivian was like everyone else who didn't take Elle seriously but she was mainly mean to her because Elle was competition. When Elle started showing more seriousness and good ethics and Warner showed bad ethics, Vivian took notice so she decided to try to be Elle's friend. Warner showed himself to be the one who wasn't serious and was instead a jerk who was okay with getting by because of his family.