British tourist detained by US authorities for 10 days over visa issue

If she is on a "four-month backpacking trip around North America" and tried to return to the US, she has exceeded the 90-day limit allowed by the Visa Waiver Program (which counts days both in the US and "adjacent territories") and is now an illegal overstayer. The unpaid labor stuff and getting refused entry to Canada is icing on the cake.

For the record, I'm no fan of ICE/CBP, but it looks like they're just enforcing the law here.

There's a right and a wrong way to enforce the law, though.

Putting her in a literal prison and in an orange jumpsuit is overkill. Clearly she just screwed up and thought what she was doing was ok, but isn't a threat. Let her go back to the UK and no longer be eligible for ESTA. How is that not sufficient?