^there's actually some irony there. She used to be stupidly sincere even about her bitchy streak (which got her into some trouble at least once) and that weird honesty made her strangely likable. Her separation from Sachi and the rest at the start of the third year however forced her to develop enough diplomatic regard for other people's feelings to bite her tongue and keep her mouth shut when necessary (witness her regular association with the Horrible Cooking Couple) - in effect engage in a degree of deception, seeing as she's hardly any less caustic on the inside. (Interesting comparisons can be made with Kuro's character developement here.)
So, in a sense, while she's grown up and been forced to learn some regard for others she's also lost her old childlike honesty in the process. (Seemed kinda relieved to be able to let her waspish tongue run free around Futaki who doesn't mind, tho...) Wonder if Sachi's picked up on that change, too?