Any car, modern or not, will kill you if you sit in your garage with the engine running long enough.....I lost an uncle via that method.
What about her mail? Were they just throwing it in a slot in the door? 6 years is a lot of junk mail.
Until the invention of catalytic converters, suicide has been committed by inhaling the exhaust fumes of a running car engine, particularly in an enclosed space such as a garage.[134][135] Before 1975, motor car exhaust contained 4–10% carbon monoxide, but newer cars have catalytic converters that eliminate over 99% of the carbon monoxide produced.[136] However, even cars with catalytic converters can produce substantial amounts of carbon monoxide if an idling car is left in an enclosed space such as a closed garage.[137] As carbon monoxide poisoning via car exhaust has become less of a suicide option, there has been an increase in new methods of carbon monoxide poisoning such as burning charcoal,[138] or fossil fuels, or by combining formic acid and sulfuric acid, within a confined space.
http://en.wikipedia.org/wiki/Carbon_monoxide_poisoning#Suicide
OTOH, it's remarkably easy to kill yourself accidentally with CO. Studies showed that a two-car garage, both large doors and a window on the other side open, with reach IDLH (Immediately Dangerous to Life and Health) concentrations in about 10 minutes. This if from operation of a 5 hp compressor.
When they say "well-ventilated," they mean well-ventilated.