The term "plot device" comes to mind when we think about Georgina Sparks. She was brought back whenever the stories were falling apart, and it got old very quick. Georgina never changed. She was always looking for revenge, and it was embarrassing by the end.
Jenny Humphrey is the kind of character most people love to hate. She started off as the good girl foil to Blair Waldorf's domineering Queen Bee. With her long golden hair and pastel clothing, she was pretty much the picture of innocence. Come Season 4 and she is the next iteration of the Evil Queen of Constance Billard. Dressed in black leather and bleach blonde everything about her as she is reintroduced seems to scream good girl gone bad. Though of course we know much of this character's makeover was due to Taylor Momsen's own personal style. Little J definitely didn't stay little for long.
[to Jenny] That's the thing. You need to be cool to be queen. Anne Boleyn thought only with her heart and she got her head chopped off. So her daughter Elizabeth made a vow never to marry a man. She married a country. Forget boys. Keep your eye on the prize, Jenny Humphrey. You can't make people love you, but you can make them fear you. For what it's worth, you're my Queen. I choose you.