Not a bad speculation of events. Other ignition sources are possible too such as a gas water heater if one were there. Starting the car might pressurize the radiator in a couple of minutes enough to spray aerosol anti-freeze onto the pilot light if it were close enough. But what knocked her out? Just backing through the garage door doesn’t bring a cause to my mind.
I might be wrong (probably am) but my impression is that there is no entrance into the house from inside the garage. Has that been established on way or another?