Question(s) for you: what actually happened at the port of entry (airport)?
1. Did they ask to see the return ticket? (It's my guess that in modern world, this is less of an issue. So easy to book one-way trips or travel on to other countries that I no longe rthink of this as a reliable indicator. Perhaps it is coming from some countries where airline sector more regulated and tickets very expensive). As an example, for anyone who also can travel to USA (has visa or esta), easy to just say you're going to fly to new york or chicage next. Tickets usually bought online and short time before.
2. Did they actually check her luggage or belongings in any way? While I don't think these things are needed much these days in physical form, I'd remind that most of the time, the passport control/secondary immigration are separate from customs. That said, yep: don't bring all of your personal belogings. Pack like it's a visit.
But good input and htanks for sharing.