I think the primary reason why Tahan is "mean" to the sisters is because they are not genuine. Their giggly, ditzy demeanor is such an affectation, and one that they can't sustain long-term, since they're constantly dropping it and acting less like over-grown three year olds. The sisters are also totally hypocritical in the way that they're constantly asserting how "nice" they are, by doing what they claim not to - bitching about Tahan. And notice how the constant waterworks (turned on mainly for Caleb's benefit) totally dried up when they had their confrontation with Tahan, showing they can hold their own and are not the infantile kewpie dolls they pretend to be. So I do not blame Tahan one bit for detesting them!
I think Tahan is an interesting character. For a girl involved in an industry where her looks are paramount, she doesn't rely on male attention for validation (hello Jade) - she isn't the least bit flirtatious. She's also shown awareness of other people's machinations, but doesn't choose to flirt or ingratiate herself with the "popular" group in an attempt to get ahead in the game. She appears to remain pretty true to herself. When you've got the sisters' on one hand playing the grotesque helpless over-grown baby card (that works a treat on Caleb) and Jade's shameless (and failed) attempts at being the femme fatale of the house on the other, props to Tahan for just being her own person, flaws and all.
