Get over yourself,’ JossI can't remember if I read it somewhere or it was in one of the commentaries I listened to but it was Joss' intent not to have Harmony change after she became a vampire. He was sort of saying that there was no real difference between a high school It girl and a soulless vampire.
I do think Harmony changed after being sired . I don't know if it was because of the way she had been turned but I liked Harmony a lot more after she became a Vamp . Plus she lasted lot longer then most of the other Vampires in the show . Plus I liked how Xander got into a slap fight with her . I bet you that one fight he never told Willow or Buffy.The perceptible difference between a mean girl (which is what she was before she was sired) and a vampire is presented as being so small that it appears that no transition has been made.
Harmony was never a leader - Cordelia calls her a sheep because she has no opinions of her own and just follows the edicts and formula of popular culture and if you ever saw the movie "Forrest Gump", that last part of the movie is dedicated to showing that everything we accept as popular culture could have been invented by someone with an IQ of 75. As a vampire, she acquires minions but she loses control of them and gets swept aside as a leader, just as she had no hope of being one when she was human. She hooks up with Spike but he treats her badly. And she has none of the martial arts sense that most vampires seem to acquire from the moment they rise. Her fight with Xander is characteristic of someone who was just as incompetent in death as she was in life.