Probably shouldn't tell border patrol you're doing unpaid labor in a country you're visiting. When speaking to authorities it's best to say the absolute minimum required for the encounter.
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I'm sure it's similar in other countries but US has always been very strict given the huge amount of people trying to work there and the very finite supply of work visas.
From my experience you'll also get extra scruntiny if you're traveling solo like this girl. I was secondary screened twice coming for business where they double checked my paperwork and TSA lady in the back asked a bunch of silly questions (like "what is PayPal").