When Zuko had first passed right by her without so much as saying a word, Katara had simply assumed he wasn't speaking to her. That was perfectly fine with her so she returned to her task with barely more than a frown at the blatant rude behavior from the supposed 'redeemed' prince. Then he'd yelled - causing her to jump and very nearly fall out of the chair she was seated in - and had dashed across the lobby and into the nearby bathroom. Wincing at what she thought was next going to be the sound of him getting ill, and trying very hard to ignore the petty urge to bend the water in the toilet so it covered him from head to toe, Katara resolutely went back to her job.
She had just started scanning the first book and double-checking the translation program was running smoothly when he offered his advice. Glancing at him (as ignoring him would be rude and she couldn't very well judge him for such things if she did the exact same), she shot him a rather unsympathetic sort of look. "If you don't know any better than to smell what you're drinking before drinking it, that's your own fault," she replied in a flat tone then turned back to the computer.
A heartbeat or so later her fingers hesitated over the keyboard and she sighed softly, shoulders slumping slightly. "Just so you know, the cranberry juice is in the smaller refrigerator over there," she made a vague motion in the direction of Cordelia's desk with one hand, the other resting on the mouse. "She moved it earlier after the last bag of blood ripped and she had to use a pitcher to store it in."
She couldn't help it. Being standoffish with Zuko was one thing. Not offering assistance with something she knew the answer to was something else entirely. Katara was angry with him, yes. She didn't trust him, true. But she didn't outright hate him, and therefore couldn't act as though she did.