You relate your own experience in UK. I can relate my
experience in
France. Background checks of criminal past are extremely unusual. What
is usual is to contact former employers (which is something I did when
we hired Sue and Mike for example).
In my experience, it's the same in the UK. I think people are failing
to consider the fact that while Wikipedia is enormous, the WMF is
tiny. Yes, she had the title "COO", but that's because she was the
only person in her department, so she had to be in charge of it. There
is a big difference between the COO of a large multinational
corporation and a solitary bookkeeper of a one-office charity.
That said, it is common practice in the UK to *ask* about criminal
background. Did anyone do that? If she outright lied to you, then it's
not really your fault. If you didn't think to ask, that's negligent.