"the author seems to assume that they are "composed" once and for all."
The singers were unlikely to accept the stilted language the early 'pretenders" used in their compositions - many of them would not have access to them anyway because of limited literacy skills, a major part of her book
She makes the interesting point that, at a later stage, rather than the singers adapting the imitations, the poets attempted to adjust their styles to folk forms.
One of the problems of all this is that the information we have from the singers, beyond the 'name, rank and serial number' stage is incredibly limited - virtually non-existant
The 'Steves' research' is based largely on speculation, what else did they have?

If you read Maidment's notes and some of Burns', Scott's and Hogg's comments, you get a different picture, but even that is bitty and largely second-hand
Our understanding of the oral tradition, with a few notable exceptions, doesn't predate the beginning of the 20th century, when the oral tradition was terminally moribund.

As for our later singers, few were asked for anything beyond the songs (in Britain and Ireland, that is); based on our own limited experience, our singers had a very different picture of their songs than the Steves.
I anybody had asked Walter Pardon, 'When the Fields Were White With Daisies' would never have been given a Roud number

Questioning these singers was extremely difficult; yo balanced a tightrope between getting information and intruding with your own ideas
When you managed it, it was extremely rewarding and informative.

'singers knew which songs were 'in the tradition'
Not really Pseudo (hate these names - they always sound as if you are being rude)
The singers we recorded described their songs as "real" and identifed with them as individuals
They saw the characters and the surroundings visually, as they sang and they identified sympathetically with teh action
I'm sure yuou know the Dillard Chamdler story of when he sang 'Little Musgrave' and punctuated it by saying "If Id been there I'd 'uv hid behind the door and shot Lord Barnard in the back when he come in".

We once carried out an experiment with a singer we became very friendly with, Traveller, Mikeen McCarthy.
We got him to sing a couple of traditional songs and asked him what hee saw when he sang them - full descriptions of people, clothes, surroundings, he told us, "we often drove pat the door of that cottage when we was tinsmithing" (he had a verse and a half only of that song
Then we got him to sing two tear-jerkers: 'I Wish all my Chidren were Babies Again and'The Night You Gave Me Back My Ring' - no pictures, nothing whatever   

Steve R's statement about literacy is simplistic - it really isn't that easy.
English and Scots Travelers are the greatest source of our ballad repertoire; both were basically 'non literate' when the oral tradition was still functioning

Sorry - I'm banging on again
Jim Carroll