I have to disagree. Maybe the folk clubs, concerts, festivals and sessions I've been going to for the last 50 years weren't "true folk", but my experience has been different. Joining in with choruses, definitely. Singing along with the verses, definitely not unless the performer has indicated it's OK.

It may be music "of for and by the people" but in my experience of hearing traditional singers in traditional settings the audience would never join in with the verses, it would be disrespectful to the singer. "Best of order" was expected and given.

I don't doubt this was upsetting for Eliza and I'm sorry for that, but I also have sympathy for her neighbour in the audience. I think what Eliza did was entirely understandable, and most of us in this situation would probably have cut her some slack in the circumstances, but it was nevertheless inappropriate behaviour for an audience member.