You pose another possible scenario. AND also that the fire Marshall’s or ATF report (factually completed and submitted) is where the answers will lie.
But to follow your thinking ...
The night before when the vehicle is parked, somehow a flammable substance leaks to the floor of garage.
SOMEHOW that ignites when she starts the vehicle and she is so startled that she hits the wall? Maybe an explosive vapor was inside the car???
I will say that a puddle of radiator fluid is NOT much of a risk of fire— even if all the water evaporated out of the solution, leaving behind a little ethylene glycol goo. Even leaked OIL is not a fire risk really. Leaking gas is of course a big fire risk.
But why does she stay in the car once a fire started? Too scared to get out perhaps? Blinded? dunno.
If you look at the Flash Point you get 111°C (231.8°F) (closed cup), and, startlingly an AUTOIGNITION temperature of a mere 410°C (770° F).
That would allow her radiator to spew antifreeze/coolant all over the interior of the engine housing, as well as the all important catalytic converter ~ BMW has had a converter in use that uses a heating coil at start up so that it works more efficiently.
That brings it up to operating temperatures well over 770° F.
So, she drives in, punches a hole in the radiator, has all kinds of evaporate fogging under the vehicle, then diddly bops out in the morning, turns on the ignition and the car bounces a little as the explosive mixture fires up when the catalytic converter housing reaches the autoignition temperature.
Not to be funny here but if you were ATF and had a choice between blaming the UNPOPULAR high intensity lights or the ENVIRONMENTAL LOBBYIST POPULAR catalytic converter with the special electrical coil that makes it even more Catalytic and Environmental friendly than lesser designs, who would a smart ATF director blame?
Hmm ~ a political decision ~ so few directions to go. Do they blame Catalyticalism or Lightbulbism?