> I will bet dollars to doughnuts that she had been warned multiple times about “risky” behavior.
Your theory lines up best with Occam's Razor: it's the more likely and simple theory, and probably true. Even so... what counts as "risky"? And the reason for her detention was having been sent something illegal from the outside. The speculation has been OTC drugs which are legal elsewhere but not in Japan. But what would that have to do with "risky" previous behavior? Granted, she missed responding to an email while she was out of country, but that hardly seems substantive either.
Honestly, it seems much more likely that she was targeted because she's visible on social media or because she's black or because she's female; or perhaps she's in some undocumented category of special contempt because she's all of those things.
On that note, I checked out her social media and she showed a property remodel and after purchasing property in Japan. It seems to me like that might show the way to others too. What better way to dissuade future immigration by simply randomly detaining folks in categories they don't like? Of course they would never do something so unseemly so as to make laws specifically disallowing blacks, single females, or even just foreigners but then again the pendulum in Japanese politics is swinging towards conservative isolationism again, no? So, it wouldn't be surprising. And if her own testimony on YouTube is to be believed and she isn't omitting anything, then I have little reason to believe any other version of this.
All that aside, and to keep this in perspective, I have no doubt that Japanese treatment of prisoners in general and even of foreigners is still by and large very good; but it's still unsettling to hear about how this was handled and about how "hostage justice" is the norm there. It seems beneath like it should be beneath them and it's very surprising to learn this about their system.