Except, as Malcolm said in 2003
"...relate to versions of The Cruel Sister, of course, which this refrain was never sung with in tradition; it was bolted on in the late 1960s, with the tune, from a 17th century English version of Riddles Wisely Expounded. That arrangement, by the band Pentangle, became very popular, and a lot of people sing it now believing it to be an authentic traditional form of the song."

So while it's a very convenient metaphor, the bent and broom really had nothing to do with the sisters, good or bad.
Robyn