Mandy won't let Aidan get another pet. She has no way of knowing whether another pet would be secretly a human. Like Schrodinger's cat, both human and animal until you open the box to check, and the only way Mandy knows to open the box is to kill the pet.
There are an awful lot of Lost Dog posters around, too. Mandy doesn't tell any of the owners where their dogs went. Or the police where the bodies she called in anonymously came from.
When Jordan's dog dies (and stays a dog), though, Mandy goes to the funeral. "I'm sorry for your loss," she tells Jordan.
"Thanks," Jordan says, sniffling.