Most likely a store employee misidentified her as a Big China resident, and Apple has a policy on NOT selling stuff to foreigners who live outside the area where they can and will provide warranty service for i-phones ~ and other stuff.
Sounds like she was a US resident.
BTW, the very devices she was purchasing are made in Big China, and as a result there's not a manager or sales geek in the company who will refuse to sell them what they ask for. If they need hacked to work in China, that service is readily available there.
The cops probably don't have a clue in this one, but folks who've been thinking about shopping in the store in Newton probably ought to go somewhere else.