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.
If any of the chars enjoy, encourage, or otherwise desire pain and suffering, they are evil.
This is an evil act. If there is a reason for it outside of personal enjoyment it could be neutral or lawful depending on reasons.
What other acts do these characters condone? A characters alignment isn’t something a single act will always be a decided by but intent is pretty clear for Natasha if not the others.
That the others allow this they are neutral to some degree. If the characters are inconsistent in their actions chaotic might be part of their alignment.
That the others invited Catherine to this life as well and are pretty okay with Natasha’s plans so I would think they also are evil.
None of the characters can be good of any kind and allow this, let alone be party to it