Good for her!
I do agree that some luck was involved to do this so quickly (good health, the financial and academic ability to earn a tough degree and then get a good job right away, and having married a person with similar benefits); but, at the same time, the couple clearly made the most of the opportunities available to them.
Personally, I'd have stayed on the job a few more years to build up a bigger buffer against inflation -- and to allow enough to raise children comfortably, though I have no idea whether that's part of their plan or not. Yes, I know that might not be everyone's idea of the right way to handle things, but in their shoes I'd have stayed in that high paying job maybe 'til 35. At age 31, she's young. She will probably be alive another 60-70 years, and a lot can change in that time.
I noted that the couple says that now they're retired, they're not tied to high-cost locations. So many people who "can't save" aren't willing to make these choices.