Barbara,
apologies for lapsing into the vernacular "slagging off" = "badmouthing".

In my world Bluegrass music is "Folk", as are cajun, old time(y), ballads, banjo tunes, fiddle tunes, blues and any material that has been around for a few generations and survived without the asistance of brainwashing by the media and their damned playlists.

I have to admit I don't know the name Cheryl Wheeler, what does she do?

I suspect (possibly incorrectly) that she is a singer/songwriter and she may be very good at what she does but I can assure you that you cannot make a claim that she is surely a folksinger by anyone's definition. As you rightly state above "What is Folk" is a never ending argument.

Billy Edd I do know (I received some audition tapes of his many years ago) and I really enjoy his work however I don't hear much/any of it now that I am aware of. Which of his songs are now performed in folk circles?

I'm looking for enlightement not an argument