Only time I ever heard Joni Mitchell live was at the folk club [Club 47?] off Harvard Square, about 1967. Her Urge For Going had been made popular by Tom Rush. If that doesn't make her a folkie, what does?
Anyway, as someone pointed out above, 'folk' is not just a North American concept or product. I'd start a discussion about British candidates for queen or king - but I'm a republican!