Steve,
> Hi Richard. I prefer the supernatural mystery of the English versions in which her body parts are used to embellish a fiddle and the fiddle sings on its own, no lover involved.

Isn't it equally supernatural in those Icelandic versions? Whether it's a harp or a fiddle, and whether only the strings are made from the murdered girl's hair or other parts are made from her finger bones etc are differences of detail. All the musician (whether he's the lover, now about to marry the dark sister, or just a passing minstrel coming to the king's hall) does is to (possibly build and) string the instrument and bring it along. In every case it's the instrument itself that identifies the sister as the murderess.