Let us calculate
Work 5 days a week, take a couple of weeks off a year, that's about 250 days. (Probably less, but 250 is a nice round number). 18 x 250 is 4500 days. divide that into a million and that's 222.22 miles per day, or about 27 miles per hour (if an 8-hour day)
27 mph doesn't sound like much, but really that's pretty fast. She has stops to make and layovers to take. 27 mph suggests to me a freeway routing, connecting towns and major transfer points. (It's a Trailways route.)
Now, alert readers may recall that a couple of days ago I drove a coack for 4-1/2 hours and completed 29 miles doing so. This seems to be typical. Even on the Mighty Number 7 you'll average about 8 miles per hour.
Let us again calculate
8 mph --> 64 miles/day --> 320 miles/week --> 16000 miles/year (and again, probably less.)
At that rate, I will be a "million-mile driver" in a mere 62 years. This other driver drives on the freeway and collects a lot of miles. I drive on city streets and collect few. But answer this: Which one of us sees more stupid shit in an 8 hour shift?
I don't mean to denigrate her achievement. Driving for 18 years free of a preventable accident is no easy feat. I've just completed 2 years accident free, so I know. But I do see colleagues with over 20 years of safe driving get little more than a shoulder patch and a coffee mug. I guess it's all "marketing" or something.