Hi, Daniel - in another thread (click), Art Thieme ties the names to three sisters. I've crosslinked all the threads in this series, Child Ballad #1 [Riddles Wisely Expounded] - see the crosslinks on the upper left of this page. I also combined this thread with another, which adds some clarification (and possibly some confusion).
Also note the similarities in Gentle Fair Jenny, although I think it's safe to say that's a different song.
-Joe Offer-