I've always believed that Amber did something to hurt Gracie that kept her from being able to find her way back, or straight up killed her. How old was Gracie when she disappeared? I forget, but as the owner of an elderly cat (16 years) I can tell you that, for the most part, they don't just bolt out the fucking door. They don't have the energy for it and prefer to sleep all day-- and if they do go out its not to climb trees, jump over fences, and certainly not to go on 'adventures' out in the dead of winter.
Either Amber has shoved more than just one cat-- alive-- into a bag and tossed the poor thing in the garbage, or she's killed them and got rid of the bodies as fast as her ""dainty"" feet allowed her. There is no other possible reason for these disappearances with this cunt. She's as psychotic as she is obese, or perhaps even more so.