Here's the UK version.
https://www.gov.uk/check-uk-visa
1) What's your nationality as shown on your passport?
2) What are you coming to the UK to do?
Tourism, including visiting friends or family
Work, academic visit or business
Study
Transit (on your way to somewhere else)
Join partner or family for a long stay
Get married or enter into a civil partnership
Visit your child at school
Get private medical treatment
For official diplomatic or government business (including transit through the UK)
Here it's pretty clear that she's coming for "work, academic visit, or business".
3) How long are you planning to work in the UK for?
Answering USA, Work, less than 6 months takes you to this page: https://www.gov.uk/check-uk-visa/y/usa/work/six_months_or_le...
That was ast updated on 9th June, so let's look at archive.org - they have 2 snapshots, one of which is from May 2015. https://web.archive.org/web/20150509170713/https://www.gov.u...
At the top, in bigger font and bolded font are the words "You may need to apply for a visa".
It links to the standard visitor visa: https://web.archive.org/web/20150518091959/https://www.gov.u...
That page says:
If you visit the UK on business
You can apply for a Standard Visitor visa if you want to visit the UK for business-related activities, eg:
you’re coming to the UK for a conference, meeting or training
and the permitted paid engagement visa:
https://web.archive.org/web/20150518091959/https://www.gov.u...No matter how it's described I can't imagine why people feel it's okay to travel to a different country to take part in a business meeting (even if that's unpaid) without either getting a visa or getting good quality legal advice.
My anger here is reserved for the conference organisers who didn't say "We don't know, let us ask a lawyer".