Of course it's meant to be humorous, but it was the house Dorothy happened to be in that killed her, not Dorothy herself. If you're in the back seat of a car and it hits and kills someone, did you kill them? And yes, there's also a driver, smart ass.
She was encouraged to do both things by every single local who knew the victim. It's pretty understandable.
EDIT: Oh, except for the victim's sister, which (witch?) is who she teamed up with three others to kill later. That's kinda questionable on the surface.
