"Her frequency #s for 1 mile diameter NEO impacts are way high."
1 every million years, doesn't seem too far off.

But in the context of comparing impacts with globe warming, I would pick a smaller rock and much higher frequency.
An impact from a rock 1 mile in diameter- wouldn't instantly kill everyone, but the direct nearly instantous death toll has no comparison. The long term affect would also unlikely kill everyone, but again there is no thing which is comparable. For example a sudden onset of an ice age, will kill lots of people within a few years- and it's far more dangerous than global warming. A mile diameter rock regardless of where it hits will kill more people- far more within hours of an impact, and then there is the long term affect, which might just be an ice age- which could follow a Earth scorched of it's vegetation and blacken sky from all burning.
I would pick a rock "around" 100 meter which occurs every 100-300 years.