Good luck to her. Cancer is the worst lottery, and even if you do everything right you can 'win' the losing ticket when those that do everything wrong don't.
We have a place in Maine and when we got the air/water quality reports from the previous exchange of owners we were stunned - the original owners had over both the Air and Water radon limits for a decade (WAY over the water one, only slightly over the ME air limit but it's nearly twice as high as MA's limit) and done nothing. In fact the water report the people we bought from got when they bought it in no uncertain terms labelled the water as 'unpotable'. A decade in a house with unpotable water and radon laced air/water, no tests. Not even an old house either. Full flight of tests is like $250 total for air and water, no idea why people just skip such an important thing.
I've seen basements in brand new houses read 100x the EPA action level. Those newer basements are much more likely to be built out to be livable, too.
We have a place in Maine and when we got the air/water quality reports from the previous exchange of owners we were stunned - the original owners had over both the Air and Water radon limits for a decade (WAY over the water one, only slightly over the ME air limit but it's nearly twice as high as MA's limit) and done nothing. In fact the water report the people we bought from got when they bought it in no uncertain terms labelled the water as 'unpotable'. A decade in a house with unpotable water and radon laced air/water, no tests. Not even an old house either. Full flight of tests is like $250 total for air and water, no idea why people just skip such an important thing.