Katrina is a rare form of shape changer called a hengeyokai. While some insist on believing that the hengeyokai are a type of lycanthrope this simply isn't true. They are closer to dopplegangers than to humans effected by a disease.
Hengeyokai are able to assume three forms - fully human, humanoid/animal and fully animal. There exist many different species, each able to assume the form of a certain type of animal. Katrina is a cat hengeyokai. In her bipedal form she looks much like a tabaxi.
Each of her three forms give Katrina different abilities. In her human form she can pass among people without them ever knowing her true race. She can also understand the language of animals when if human form. In her cat form she has excellent infravision, out to 120', and attacks as a normal house cat. Finally in her bipedal form she retains her infravision, can speak in both the human and animal tongues, and can use her claws while in combat. This gives her +1 to all attacks when she uses her martial arts style.
Katrina can change back and forth between forms once per day per level. The change has no effect on her other than to change her morphology.