It appears she is in a divorce deal and she and her boyfriend were motivated by hate and spite for her husband, to kill the dog in an effort to, “Get back at him” or “Pay him back”. It was apparently the husbands dog.
It’s why they were drinking and were photographed with bottle of alcohol and were smiling and laughing. Sick sick.
The ex says that he thought he had a decent platonic relationship with her- if there was any anger or hatred on her part he wasn’t aware of it at all. That was one reason he approached her about taking the dog.
So while it may turn out to be the motive the revenge killing looks bizarre, like it came out of nowhere. As does her claiming it was her “therapy dog” when that was easily disprovable, and the renaming of the dog, and denying it had ever been her ex’s dog. And deciding to kill it when she could have turned it loose or in to the pound. Everything she did regarding the dog has a crazy feel to it.
Someone upthread suggested that it could be bipolar behavior rather than schizophrenia since that would fit the planning and reasoning ability. I’m not trying to make an excuse for her, just trying to figure out what was going on from the information we have.