Really? I'm on the fence about her. I think her testifying against her brother was totally badass, but her innocence schtick wears thin, too.
I forgot about another worst: Marisol. Dude, she was a straight-up terrible person to everyone, including Katie. From telling everyone Katie was bulimic, to throwing Fiona under the bus about the foiling the caf situation, to jumping to the conclusion that Mo was a drug addict and then acting like an asshole towards him, to just generally being a snot, Marisol was loathsome. The fact that anyone was pleasant to her made me dislike all the other characters as well. I think Drew as a character is sort of a potato, but he was sure as shit right about Marisol being gross.