When you volunteer a lot of information you come across as nervous, and sketchy
When you volunteer a lot of information you come across as nervous, and sketchy
Innocent people should not have to avoid being truthful or complete in their answers just to avoid arousing "suspicion". Innocent people should not have to know ahead-of-time that giving honest and complete answers to an official will lead to this kind of treatment. This kind of treatment should not be acceptable under any circumstances for people who are actually innocent and/or have not done anything that would cause suspicion in a reasonable person. Giving complete answers is not reasonable grounds for suspicion.
What you're saying may be good advice in practical terms, but implying it's a sensible default is basically surrendering to an insane, broken system.
I question your statement that she "certainly" was violating the law. She and the conference organizers had researched the situation beforehand and attempted to obtain the correct visa. The publicly available information about the visa programs did not specify that the nationality of the company sponsoring the conference made a difference. You state "the reason that she had for entering the UK did require a visa that she had to obtain before traveling" but according to her research after the fact the truth is that the reason that she had for entering the UK was not supported by any sort of visa.
And even if there would have been no appropriate visa to apply for that means the UK does not want those people in. Turning up at the border and requesting entry based on a reason not allowed on the visa-free program is not a solution no matter how wrong the situation feels.
Moral responsibility and causality are two different things.
The other thing about volunteering extra information is it can come back to bite you if you're not consistent next time, so I also try being as vague but still truthful as possible. If I was visiting anywhere else but Canada, though, I wouldn't have any problems skipping the whole drama with "I'm traveling for a vacation" and "nope, not meeting anyone I know" regardless of whether that is true or not.
Border crossing is basically a hazing ritual in a lot of places, and while I agree with GP's "this was her mistake" it really is dumb we all have to put up with the hazing. Kind of like not bribing a cop in [insert south american nation here] who is giving you trouble, or bribing him with way too much money. Some people just don't get that there are dumb, sucky customs where not following them (or trying to follow what they think is the most honest or rational process) is a mistake and complaining about the mistake after the fact won't solve anything.
Interestingly enough, me and my colleagues were pulled aside for additional questioning because two of us didn't own cars (we both live in Seattle and bus everywhere). For some reason the Canadian border agent simply didn't believe that people in the US don't own cars! We were able to go through after the manager of the team we were going to meet had been called to verify our story.