Definitely
Katherine.
Katherine was around far longer than
Kathleen, which I believe is a surname.
Kathleen also sounds like a name someone going through a mid-life crisis would have(sorry all you kathleens).
Kathleen. It sounds like a lean calf- a name for an animal maybe but not for a girl. But hey, if you're gonna call her
Kat she might as well have the name
Kathleen, so no matter what you call her it just refers back to animals.