I haven't followed this case, and certainly do not know all the details. So bare with me. Is t thit known if she stopped anywhere near where she crashed? Like to get gas, or go to the restroom? Because if she did, I wonder if someone didn't put that rag in the tailpipe then. I don't think it was in the actual muffler. You would have needed a broom stick or something similar to push a rag through the tail pipe into the muffler.
From what little I know about vehicles, a rag in the tail pipe would affect it's performance. It doesn't get air from the tail pipe, but from the air filter on the motor, but what goes in, must come out, so the air leaves through the exhaust. I can't imagine someone driving like that. And I can't see any reasonable reason to put it in the tailpipe after it's crashed. If the tail pipe was hot, and releasing 'smoke' or condensation, then you'd burn yourself trying to stuff something into it.
I recently saw this one some TV show, and it just doesn't make sense. Maura's disappearance. I would have thought suicide, but then, why no one has found her body? Of course now, unless someone saw a skull, they probably wouldn't even know it's a person.
Such a bizarre case!