In this case, Natasha and her friends.
Natasha is one of the “owners” of Catherine, who she decides to treat as a “pet” because she reminds her of a cat (hence the name CATherine). Natasha and her friends invite Catherine into the friend group and they all live together, but Catherine is treated badly there and Natasha makes a plan to kill Catherine.
She doesn’t see Catherine as a person, but as an actual animal, a tool, and a nuisance, and wants to badly mistreat her which ends up traumatizing her.
Yay, thanks! Catherine started out as really kind and sweet, then she turned to have a sweet façade, a messy, traumatized interior, and underneath that, a kind and sweet “core”