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?

There is only one way to enforce the law, which is to enforce it upon learning of all the circumstances, both in favour and not in favour of the accused. The fact that you are not familiar with the law never protects you by design ("oh sorry, I never realised I wasn't allowed to just take their bike and ride away") — so it's upon the courts to make judgement on the entire set of circumstances.

The problem with any immigration service in the world is that they are dealing with non-citizens which lack most protections citizenship would have given them — which means that it may take its sweet time before courts actually hear her defense and probably decide as you suggest (along with introducing a 3 or 5 year ban on entering the US).

All people involved have jurisdiction on how to apply the law. Putting this girl in prison and a jumpsuit is ridiculous.

It creates yet another person who will come to rightfully hate the US, gets bad press affecting tourism and business, and for what? For a girl that loved the US, misinterpreted or misunderstood something and is staying a little longer, spending more money and having good experiences.

Enforce the law, sure, whatever, but the jumpsuit and 10 days in a detention center are barbaric and unnecessary. There's a reason this wouldn't have happened before a wannabe dictator was in power.

Don't worry they do it to citizens too. On one occasion CBP told me they would not let me enter the country. On another they imprisoned me for ~12 hours, on another they asked me if I work in the US and tried to demand ever more intrusive questions about it.

... I am us citizen presenting with us passport, look and talk extremely white with no foreign accent.

How did your situation resolve? Did you sue them?