What then?
Immediately following that event the two have Carl's rotting corpse to attend to. The cops don't know it's self-defense and with Oda Mae's record, well, it's not looking good for either of them. Surely an arrest, trial maybe who knows?
Then what happens?
What, after the Nintendo game kit?
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Carl's death was accidental, no way Molly or Oda Mae would get accused of pushing him down and slamming the window down on him.
If there were an investigation, it might show Carl's role in illegal money-laundering, but the whole point of going through Carl was to hide money. Unless someone explicitly told the police to look into each of Carl's accounts, there'd be no reason to look into Rita Wilson in particular, especially since Lyle Ferguson can vouch for Rita being an actual person.