Howdy Glen. I can't much help you with your window problems,
But as for the smell of burnt plastic, I can. I bought my '91 Explorer from a man whose wife called it "the rolling ash tray". The husband smoked quite a bit. My mom suggested an old method of clearing out the cigarette smell. She suggested setting an open bowl of fresh coffee grounds on the floorboard, as close to the center of the cabin as possible, for a few days. I used a Tupperware bowl for the coffee grounds in my Explorer so that whenever I needed to drive it, I just snapped the lid back on the bowl, and drove away.
It'll take at least three days to lessen a pungent odor to a smell that's tolerable (at least in a cabin with as much volume as an Explorer's). If you're worried about your mother in law sending an avalanche of coffee grounds skidding across her floor boards, then I would suggest putting the coffee grounds in the Crown Vic over a weekend, or whenever she might have a good two days without any need of the car, and repeating that as many times as may be needed.
In the end, it
did not leave the interior smelling like a caffeine-crazed coffee maniac's dream-mobile at all

. Any coffee smell that might remain will leave the vehicle with as little as driving with all (or most of) the windows down for a day. Seeing as how this might not be entirely possible in the Winter, a cheap air freshener or a shot of Frebreeze can take care of coffee's scent a lot more easily than it will the smell of burnt plastic.