Keyless ignition gives us the answer to the question of how it is she was in the driver's seat with the garage doors still closed.
The answer is she didn't intend to start the car ~ but that happened anyway.
Things like gasoline have a very strong smell and the propane we buy as well as natural gas has a chemical added to it to make it smell real bad to allow people to know when it is leaking.
Antifreeze does not. Dogs will lick pools of it and make themselves sick. Some say it smells sweet, like maple syrup.
People use it poison others because it does not taste that bad.
I could see her entering the garage in the morning and not smelling anything that “smelled” explosive and not being alerted to any danger.