Okay, in summary of my articles on the origins of the ballad which ought to be read fully and carefully to weigh up the fairly straightforward evidence: I've never met anyone who didn't think that CFS was a straight rewrite of Bramble Briar from the early 19th century, the work of a broadside hack.

There are too many points of co-incidence to clearly demonstrate that the ballad in its earliest extant forms is directly taken from an English translation of the Isabella story. Since Belden's time everyone who has looked at the ballad in any detail has come to that conclusion even without access to the longer versions.

Whilst the original broadside hasn't yet come to light, or perhaps hasn't survived, a garland ballad printed in Bristol in the mid 18th century has 3 stanzas at the start which are so close to the early stanzas in Bramble Briar that this could not be a co-incidence. So either they were by the same writer, or one influenced the other.

An extra interesting point to me is that when I first came across the long versions I actually considered the ballad could have originated in America. There are Bridg(e)waters in almost all of the eastern seaboard states. It was the finding of the Bristol garland that swayed me back to Somerset/Bristol as the setting and original.