Any character can orb walk by simply walking back and forth or moving in some kind of pattern. Kallista cannot autoattack and orb walk together. The moment u attack and try to move your character, kallista will automatically leap instead. She has 2 animations: attack animation and leap animation. You can't cancel either of these. You can autoattack without leaping. If you want to move kallista without leaping, after she finishes her attack animation, press "s" (or your designated hotkey to stop your character) then move your character.
In my experience with kallista, its much better just to utilize the leap animation or let her autoattack in one spot.