We don't really know why she did it. I mean, we're just assuming it was a random thing. Maybe that damn cat kept her up all night like cats sometimes do with their kitty orgies. Or maybe she knows the cat's owner, and hates her. Or maybe the cat mumbled something anti-Semitic. We don't know. Either way, it was an extreme reaction. A reaction on par with what future serial killers would do? No.
I remember this dude who lived on my block named Smokey, took all these kittens and tossed em off the top of his building to see if they would land on their feet. Now that guy was a sociopath. (Which would explain why he grew up to become and killer and is currently serving 25 to life.) Tossing a cat into a trash can? Eh.